diff --git a/ui/web/src/lib/constants.ts b/ui/web/src/lib/constants.ts
index 470a9c40..d70e3330 100644
--- a/ui/web/src/lib/constants.ts
+++ b/ui/web/src/lib/constants.ts
@@ -74,3 +74,27 @@ export const TIMEZONE_OPTIONS = [
   { value: "Asia/Singapore", label: "Singapore (SGT)" },
   { value: "Australia/Sydney", label: "Sydney (AEST)" },
 ] as const;
+
+/** IANA timezones for server-side scheduling (cron, heartbeat). */
+export const IANA_TIMEZONES = [
+  { value: "UTC", label: "UTC" },
+  { value: "Asia/Ho_Chi_Minh", label: "Asia/Ho_Chi_Minh (UTC+7)" },
+  { value: "Asia/Bangkok", label: "Asia/Bangkok (UTC+7)" },
+  { value: "Asia/Shanghai", label: "Asia/Shanghai (UTC+8)" },
+  { value: "Asia/Tokyo", label: "Asia/Tokyo (UTC+9)" },
+  { value: "Asia/Seoul", label: "Asia/Seoul (UTC+9)" },
+  { value: "Asia/Singapore", label: "Asia/Singapore (UTC+8)" },
+  { value: "Asia/Kolkata", label: "Asia/Kolkata (UTC+5:30)" },
+  { value: "Asia/Dubai", label: "Asia/Dubai (UTC+4)" },
+  { value: "Europe/London", label: "Europe/London (UTC+0)" },
+  { value: "Europe/Paris", label: "Europe/Paris (UTC+1)" },
+  { value: "Europe/Berlin", label: "Europe/Berlin (UTC+1)" },
+  { value: "Europe/Moscow", label: "Europe/Moscow (UTC+3)" },
+  { value: "America/New_York", label: "America/New_York (UTC-5)" },
+  { value: "America/Chicago", label: "America/Chicago (UTC-6)" },
+  { value: "America/Denver", label: "America/Denver (UTC-7)" },
+  { value: "America/Los_Angeles", label: "America/Los_Angeles (UTC-8)" },
+  { value: "America/Sao_Paulo", label: "America/Sao_Paulo (UTC-3)" },
+  { value: "Australia/Sydney", label: "Australia/Sydney (UTC+11)" },
+  { value: "Pacific/Auckland", label: "Pacific/Auckland (UTC+13)" },
+] as const;
diff --git a/ui/web/src/pages/agents/agent-detail/heartbeat-config-dialog.tsx b/ui/web/src/pages/agents/agent-detail/heartbeat-config-dialog.tsx
index 1519a1b9..4a5e900d 100644
--- a/ui/web/src/pages/agents/agent-detail/heartbeat-config-dialog.tsx
+++ b/ui/web/src/pages/agents/agent-detail/heartbeat-config-dialog.tsx
@@ -18,6 +18,7 @@ import { useChannels } from "@/pages/channels/hooks/use-channels";
 import { useProviders } from "@/pages/providers/hooks/use-providers";
 import { useUiStore } from "@/stores/use-ui-store";
 import { ProviderModelSelect } from "@/components/shared/provider-model-select";
+import { IANA_TIMEZONES } from "@/lib/constants";
 import type { HeartbeatConfig, DeliveryTarget } from "@/pages/agents/hooks/use-agent-heartbeat";
 
 interface HeartbeatConfigDialogProps {
@@ -54,7 +55,7 @@ export function HeartbeatConfigDialog({
   const [intervalMin, setIntervalMin] = useState(30);
   const [ackMaxChars, setAckMaxChars] = useState(300);
   const [maxRetries, setMaxRetries] = useState(2);
-  const [isolatedSession, setIsolatedSession] = useState(true);
+  const [isolatedSession, setIsolatedSession] = useState(false);
   const [lightContext, setLightContext] = useState(false);
   const [activeHoursStart, setActiveHoursStart] = useState("");
   const [activeHoursEnd, setActiveHoursEnd] = useState("");
@@ -182,7 +183,7 @@ export function HeartbeatConfigDialog({
                 min={5}
                 value={intervalMin}
                 onChange={(e) => setIntervalMin(Math.max(5, Number(e.target.value) || 5))}
-                className="w-24 text-center text-base md:text-sm"
+                className="w-[4.5rem] text-center text-base md:text-sm"
               />
               <span className="text-xs text-muted-foreground">min</span>
             </div>
@@ -298,8 +299,8 @@ export function HeartbeatConfigDialog({
                 {t("heartbeat.sectionSchedule")}
               </h4>
             </div>
-            <div className="grid grid-cols-1 gap-3 sm:grid-cols-3">
-              <div className="space-y-1">
+            <div className="flex flex-wrap items-end gap-3">
+              <div className="space-y-1 w-24">
                 <Label htmlFor="hb-start" className="text-xs">{t("heartbeat.activeHoursStart")}</Label>
                 <Input
                   id="hb-start"
@@ -309,7 +310,7 @@ export function HeartbeatConfigDialog({
                   className="text-base md:text-sm"
                 />
               </div>
-              <div className="space-y-1">
+              <div className="space-y-1 w-24">
                 <Label htmlFor="hb-end" className="text-xs">{t("heartbeat.activeHoursEnd")}</Label>
                 <Input
                   id="hb-end"
@@ -319,15 +320,19 @@ export function HeartbeatConfigDialog({
                   className="text-base md:text-sm"
                 />
               </div>
-              <div className="space-y-1">
-                <Label htmlFor="hb-tz" className="text-xs">{t("heartbeat.timezone")}</Label>
-                <Input
-                  id="hb-tz"
-                  placeholder="Asia/Ho_Chi_Minh"
-                  value={timezone}
-                  onChange={(e) => setTimezone(e.target.value)}
-                  className="text-base md:text-sm"
-                />
+              <div className="space-y-1 flex-1 min-w-[160px]">
+                <Label className="text-xs">{t("heartbeat.timezone")}</Label>
+                <Select value={timezone || "__auto__"} onValueChange={(v) => setTimezone(v === "__auto__" ? "" : v)}>
+                  <SelectTrigger className="text-base md:text-sm">
+                    <SelectValue />
+                  </SelectTrigger>
+                  <SelectContent>
+                    <SelectItem value="__auto__">{defaultTz}</SelectItem>
+                    {IANA_TIMEZONES.map((tz) => (
+                      <SelectItem key={tz.value} value={tz.value}>{tz.label}</SelectItem>
+                    ))}
+                  </SelectContent>
+                </Select>
               </div>
             </div>
             <p className="text-xs text-muted-foreground">{t("heartbeat.scheduleHint")}</p>
diff --git a/ui/web/src/pages/config/sections/cron-section.tsx b/ui/web/src/pages/config/sections/cron-section.tsx
index fba9caf6..23a4fdaa 100644
--- a/ui/web/src/pages/config/sections/cron-section.tsx
+++ b/ui/web/src/pages/config/sections/cron-section.tsx
@@ -6,29 +6,7 @@ import { Input } from "@/components/ui/input";
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "@/components/ui/card";
 import { InfoLabel } from "@/components/shared/info-label";
-
-const TIMEZONES = [
-  { value: "UTC", label: "UTC" },
-  { value: "Asia/Ho_Chi_Minh", label: "Asia/Ho_Chi_Minh (UTC+7)" },
-  { value: "Asia/Bangkok", label: "Asia/Bangkok (UTC+7)" },
-  { value: "Asia/Shanghai", label: "Asia/Shanghai (UTC+8)" },
-  { value: "Asia/Tokyo", label: "Asia/Tokyo (UTC+9)" },
-  { value: "Asia/Seoul", label: "Asia/Seoul (UTC+9)" },
-  { value: "Asia/Singapore", label: "Asia/Singapore (UTC+8)" },
-  { value: "Asia/Kolkata", label: "Asia/Kolkata (UTC+5:30)" },
-  { value: "Asia/Dubai", label: "Asia/Dubai (UTC+4)" },
-  { value: "Europe/London", label: "Europe/London (UTC+0)" },
-  { value: "Europe/Paris", label: "Europe/Paris (UTC+1)" },
-  { value: "Europe/Berlin", label: "Europe/Berlin (UTC+1)" },
-  { value: "Europe/Moscow", label: "Europe/Moscow (UTC+3)" },
-  { value: "America/New_York", label: "America/New_York (UTC-5)" },
-  { value: "America/Chicago", label: "America/Chicago (UTC-6)" },
-  { value: "America/Denver", label: "America/Denver (UTC-7)" },
-  { value: "America/Los_Angeles", label: "America/Los_Angeles (UTC-8)" },
-  { value: "America/Sao_Paulo", label: "America/Sao_Paulo (UTC-3)" },
-  { value: "Australia/Sydney", label: "Australia/Sydney (UTC+11)" },
-  { value: "Pacific/Auckland", label: "Pacific/Auckland (UTC+13)" },
-];
+import { IANA_TIMEZONES } from "@/lib/constants";
 
 interface CronData {
   max_retries?: number;
@@ -80,7 +58,7 @@ export function CronSection({ data, onSave, saving }: Props) {
             </SelectTrigger>
             <SelectContent>
               <SelectItem value="__system__">{t("cron.defaultTimezonePlaceholder")}</SelectItem>
-              {TIMEZONES.map((tz) => (
+              {IANA_TIMEZONES.map((tz) => (
                 <SelectItem key={tz.value} value={tz.value}>{tz.label}</SelectItem>
               ))}
             </SelectContent>