diff --git a/deploy/nixos/configuration.nix b/deploy/nixos/configuration.nix
index 6c11db7..3d62d54 100644
--- a/deploy/nixos/configuration.nix
+++ b/deploy/nixos/configuration.nix
@@ -46,8 +46,9 @@
     };
   };
 
-  # Timezone - set to your location
-  time.timeZone = "America/Guatemala";
+  # Fleet default. Override per machine with timeZoneForModel in flake.nix —
+  # mkDefault is what lets that override win without mkForce.
+  time.timeZone = lib.mkDefault "America/Guatemala";
 
   # Locale
   i18n.defaultLocale = "en_US.UTF-8";
diff --git a/flake.nix b/flake.nix
index 194ca55..73b6b2f 100644
--- a/flake.nix
+++ b/flake.nix
@@ -67,6 +67,18 @@
         batm3 = "USD";
       };
 
+      # Timezone per machine model. Wall-clock time on an ATM is not cosmetic:
+      # it is what the journal is read in when someone is standing at the
+      # machine, and system.autoUpgrade's `dates = "04:00"` is local, so this
+      # decides when the nightly rebuild restarts the app and the dispenser
+      # runs its audible init routine. A machine on the wrong zone does that
+      # in the middle of its own business hours.
+      #
+      # Unlisted models fall back to the fleet default in configuration.nix.
+      timeZoneForModel = {
+        sintra = "Europe/Paris";
+      };
+
       lib = nixpkgs.lib;
 
       # Helper to create a live USB NixOS config for a specific machine model
@@ -124,6 +136,10 @@
                 appDir = "${atm-app}";
               };
 
+              # Per-machine wall clock; see timeZoneForModel above.
+              time.timeZone = lib.mkIf (timeZoneForModel ? ${machineModel})
+                timeZoneForModel.${machineModel};
+
               # Operator TUI and CLI tools
               environment.systemPackages = [
                 atm-tui.packages.${system}.default