add timer

services/timer.nix

@@ -0,0 +1,18 @@
+{ config, pkgs, ... }: {
+  systemd.services.auto-shutdown = {
+    description = "Automatic daily shutdown at 9:30 pm";
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = [ "${pkgs.systemd}/bin/systemctl poweroff" ];
+    };
+  };
+
+  systemd.timers.auto-shutdown = {
+    description = "Timer for daily shutdown at 9:30 pm";
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnCalendar = "21:40";
+      Persistent = true;
+    };
+  };
+}