diff --git a/backend/scheduler.py b/backend/scheduler.py
index 9aeeae4..2d1a9c0 100644
--- a/backend/scheduler.py
+++ b/backend/scheduler.py
@@ -26,7 +26,7 @@ import logging
 import os
 import threading
 import uuid
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 from pathlib import Path
 from typing import Any
 
@@ -118,7 +118,7 @@ def _validate_schedule(schedule: dict[str, Any]) -> dict[str, Any]:
     try:
         parsed = datetime.fromisoformat(at)
         if parsed.tzinfo is None:
-            parsed = parsed.replace(tzinfo=timezone.utc)
+            parsed = parsed.replace(tzinfo=UTC)
     except ValueError:
         raise ValueError("at doit être une date ISO-8601 (ex. 2026-10-05T08:30:00)") from None
     return {"kind": kind, "at": parsed.isoformat()}
@@ -138,7 +138,7 @@ def create_task(
     """Create a scheduled task. Raises ValueError on invalid action/schedule."""
     validated_action = _validate_action(action)
     validated_schedule = _validate_schedule(schedule)
-    now = datetime.now(timezone.utc)
+    now = datetime.now(UTC)
     with _lock:
         tasks = _read_tasks()
         task = {
@@ -200,9 +200,9 @@ def delete_task(task_id: str) -> bool:
 
 def compute_next_run(task: dict[str, Any], now: datetime | None = None) -> datetime:
     """Compute the next due datetime for *task*."""
-    now = now or datetime.now(timezone.utc)
+    now = now or datetime.now(UTC)
     if now.tzinfo is None:
-        now = now.replace(tzinfo=timezone.utc)
+        now = now.replace(tzinfo=UTC)
     schedule = task.get("schedule", {})
     kind = schedule.get("kind")
     last_run_at = task.get("last_run_at")
@@ -211,7 +211,7 @@ def compute_next_run(task: dict[str, Any], now: datetime | None = None) -> datet
         try:
             last = datetime.fromisoformat(str(last_run_at))
             if last.tzinfo is None:
-                last = last.replace(tzinfo=timezone.utc)
+                last = last.replace(tzinfo=UTC)
         except ValueError:
             last = None
     if kind == "interval_hours":
@@ -233,11 +233,11 @@ def compute_next_run(task: dict[str, Any], now: datetime | None = None) -> datet
         try:
             at = datetime.fromisoformat(str(schedule.get("at")))
             if at.tzinfo is None:
-                at = at.replace(tzinfo=timezone.utc)
+                at = at.replace(tzinfo=UTC)
         except ValueError:
             return now
         if task.get("last_run_at"):
-            return datetime.max.replace(tzinfo=timezone.utc)  # déjà exécutée
+            return datetime.max.replace(tzinfo=UTC)  # déjà exécutée
         return at
     return now + timedelta(hours=24)
 
@@ -278,7 +278,7 @@ def run_task(task_id: str, *, manual: bool = False) -> dict[str, Any]:
             return {"task_id": task_id, "skipped": True, "reason": "disabled"}
         try:
             result = _execute_action(task)
-            task["last_run_at"] = datetime.now(timezone.utc).isoformat()
+            task["last_run_at"] = datetime.now(UTC).isoformat()
             task["last_status"] = "ok"
             task["last_error"] = None
             task["run_count"] = int(task.get("run_count", 0)) + 1
@@ -292,7 +292,7 @@ def run_task(task_id: str, *, manual: bool = False) -> dict[str, Any]:
                 broadcast("schedule_success", f"Tâche « {task['name']} » OK", "Exécution manuelle réussie.")
             return {"task_id": task_id, "ok": True, "result": result}
         except Exception as e:
-            task["last_run_at"] = datetime.now(timezone.utc).isoformat()
+            task["last_run_at"] = datetime.now(UTC).isoformat()
             task["last_status"] = "error"
             task["last_error"] = str(e)
             task["run_count"] = int(task.get("run_count", 0)) + 1
@@ -315,7 +315,7 @@ def run_task(task_id: str, *, manual: bool = False) -> dict[str, Any]:
 
 def tick(now: datetime | None = None) -> list[dict[str, Any]]:
     """Run every due task. Returns per-task outcomes (empty when idle)."""
-    now = now or datetime.now(timezone.utc)
+    now = now or datetime.now(UTC)
     outcomes: list[dict[str, Any]] = []
     for task in _read_tasks():
         if not task.get("enabled", True):
@@ -323,7 +323,7 @@ def tick(now: datetime | None = None) -> list[dict[str, Any]]:
         try:
             next_run = datetime.fromisoformat(str(task.get("next_run_at") or ""))
             if next_run.tzinfo is None:
-                next_run = next_run.replace(tzinfo=timezone.utc)
+                next_run = next_run.replace(tzinfo=UTC)
         except ValueError:
             next_run = compute_next_run(task, now)
         if next_run <= now: