diff --git a/src/components/ClientMonitor/ClientMonitorPage.tsx b/src/components/ClientMonitor/ClientMonitorPage.tsx
index eaebdc6..681f1fc 100644
--- a/src/components/ClientMonitor/ClientMonitorPage.tsx
+++ b/src/components/ClientMonitor/ClientMonitorPage.tsx
@@ -27,7 +27,17 @@ import Search from "@mui/icons-material/Search";
 import PageTitleBar from "@/components/PageTitleBar";
 import { NEXT_PUBLIC_API_URL } from "@/config/api";
 import { clientAuthFetch } from "@/app/utils/clientAuthFetch";
+import { arrayToDateTimeString } from "@/app/utils/formatUtil";
 import dayjs from "dayjs";
+
+function formatApiDateTime(value: unknown): string {
+  if (value == null) return "—";
+  if (Array.isArray(value)) {
+    return arrayToDateTimeString(value as (number | undefined)[]);
+  }
+  const d = dayjs(value as string | number);
+  return d.isValid() ? d.format("YYYY-MM-DD HH:mm:ss") : "—";
+}
 import PrinterMonitorTab from "@/components/ClientMonitor/PrinterMonitorTab";
 
 type ClientRow = {
@@ -383,17 +393,17 @@ export default function ClientMonitorPage() {
                         </TableCell>
                         <TableCell>
                           {formatAgo(row.secondsSinceHeartbeat)}
-                          {row.lastHeartbeat && (
-                            <Typography variant="caption" display="block" color="text.secondary">
-                              {dayjs(row.lastHeartbeat).format("HH:mm:ss")}
-                            </Typography>
-                          )}
-                        </TableCell>
-                        <TableCell>
-                          {row.lastActivity
-                            ? dayjs(row.lastActivity).format("HH:mm:ss")
-                            : "—"}
+                      {row.lastHeartbeat && (
+                        <Typography variant="caption" display="block" color="text.secondary">
+                          {formatApiDateTime(row.lastHeartbeat).slice(11)}
+                        </Typography>
+                      )}
                         </TableCell>
+                    <TableCell>
+                      {row.lastActivity
+                        ? formatApiDateTime(row.lastActivity).slice(11)
+                        : "—"}
+                    </TableCell>
                       </TableRow>
                     );
                   })
@@ -528,11 +538,7 @@ export default function ClientMonitorPage() {
                     const st = STATUS_LABEL[row.status] ?? STATUS_LABEL.offline;
                     return (
                       <TableRow key={`${row.id ?? row.recordedAt}-${row.deviceId}`} hover>
-                        <TableCell>
-                          {row.recordedAt
-                            ? dayjs(row.recordedAt).format("YYYY-MM-DD HH:mm:ss")
-                            : "—"}
-                        </TableCell>
+                        <TableCell>{formatApiDateTime(row.recordedAt)}</TableCell>
                         <TableCell>
                           <Chip size="small" color={st.color} label={st.label} />
                         </TableCell>
diff --git a/src/components/ClientMonitor/PrinterMonitorTab.tsx b/src/components/ClientMonitor/PrinterMonitorTab.tsx
index adc0b86..a07cfa3 100644
--- a/src/components/ClientMonitor/PrinterMonitorTab.tsx
+++ b/src/components/ClientMonitor/PrinterMonitorTab.tsx
@@ -16,8 +16,18 @@ import {
 } from "@mui/material";
 import { NEXT_PUBLIC_API_URL } from "@/config/api";
 import { clientAuthFetch } from "@/app/utils/clientAuthFetch";
+import { arrayToDateTimeString } from "@/app/utils/formatUtil";
 import dayjs from "dayjs";
 
+function formatApiDateTime(value: unknown): string {
+  if (value == null) return "—";
+  if (Array.isArray(value)) {
+    return arrayToDateTimeString(value as (number | undefined)[]);
+  }
+  const d = dayjs(value as string | number);
+  return d.isValid() ? d.format("YYYY-MM-DD HH:mm:ss") : "—";
+}
+
 type PrinterRow = {
   id: number;
   code?: string;
@@ -172,11 +182,7 @@ export default function PrinterMonitorTab({ active, refreshAt = 0 }: Props) {
                         {row.errorMessage ?? "無法連線"}
                       </Typography>
                     </TableCell>
-                    <TableCell>
-                      {row.lastCheckAt
-                        ? dayjs(row.lastCheckAt).format("YYYY-MM-DD HH:mm:ss")
-                        : "—"}
-                    </TableCell>
+                    <TableCell>{formatApiDateTime(row.lastCheckAt)}</TableCell>
                   </TableRow>
                 ))}
               </TableBody>
@@ -241,11 +247,7 @@ export default function PrinterMonitorTab({ active, refreshAt = 0 }: Props) {
                     <TableCell align="right">
                       {row.latencyMs != null ? row.latencyMs : "—"}
                     </TableCell>
-                    <TableCell>
-                      {row.lastCheckAt
-                        ? dayjs(row.lastCheckAt).format("YYYY-MM-DD HH:mm:ss")
-                        : "—"}
-                    </TableCell>
+                    <TableCell>{formatApiDateTime(row.lastCheckAt)}</TableCell>
                   </TableRow>
                 );
               })