diff --git a/nixos/modules/services/backup/btrbk.nix b/nixos/modules/services/backup/btrbk.nix
index 0c00b934405..a761e65f5ed 100644
--- a/nixos/modules/services/backup/btrbk.nix
+++ b/nixos/modules/services/backup/btrbk.nix
@@ -51,6 +51,8 @@ let
     '';
 in
 {
+  meta.maintainers = with lib.maintainers; [ oxalica ];
+
   options = {
     services.btrbk = {
       extraPackages = lib.mkOption {
@@ -76,9 +78,12 @@ in
             submodule {
               options = {
                 onCalendar = lib.mkOption {
-                  type = lib.types.str;
+                  type = lib.types.nullOr lib.types.str;
                   default = "daily";
-                  description = "How often this btrbk instance is started. See systemd.time(7) for more information about the format.";
+                  description = ''
+                    How often this btrbk instance is started. See systemd.time(7) for more information about the format.
+                    Setting it to null disables the timer, thus this instance can only be started manually.
+                  '';
                 };
                 settings = lib.mkOption {
                   type = let t = lib.types.attrsOf (lib.types.either lib.types.str (t // { description = "instances of this type recursively"; })); in t;
@@ -214,7 +219,8 @@ in
           };
         }
       )
-      cfg.instances;
+      (lib.filterAttrs (name: instance: instance.onCalendar != null)
+        cfg.instances);
   };
 
 }
diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
index 0c085b64efa..b904660a691 100644
--- a/nixos/tests/all-tests.nix
+++ b/nixos/tests/all-tests.nix
@@ -62,6 +62,7 @@ in
   breitbandmessung = handleTest ./breitbandmessung.nix {};
   brscan5 = handleTest ./brscan5.nix {};
   btrbk = handleTest ./btrbk.nix {};
+  btrbk-no-timer = handleTest ./btrbk-no-timer.nix {};
   buildbot = handleTest ./buildbot.nix {};
   buildkite-agents = handleTest ./buildkite-agents.nix {};
   caddy = handleTest ./caddy.nix {};
diff --git a/nixos/tests/btrbk-no-timer.nix b/nixos/tests/btrbk-no-timer.nix
new file mode 100644
index 00000000000..4fcab8839c8
--- /dev/null
+++ b/nixos/tests/btrbk-no-timer.nix
@@ -0,0 +1,37 @@
+import ./make-test-python.nix ({ lib, pkgs, ... }:
+  {
+    name = "btrbk-no-timer";
+    meta.maintainers = with lib.maintainers; [ oxalica ];
+
+    nodes.machine = { ... }: {
+      environment.systemPackages = with pkgs; [ btrfs-progs ];
+      services.btrbk.instances.local = {
+        onCalendar = null;
+        settings.volume."/mnt" = {
+          snapshot_dir = "btrbk/local";
+          subvolume = "to_backup";
+        };
+      };
+    };
+
+    testScript = ''
+      start_all()
+
+      # Create btrfs partition at /mnt
+      machine.succeed("truncate --size=128M /data_fs")
+      machine.succeed("mkfs.btrfs /data_fs")
+      machine.succeed("mkdir /mnt")
+      machine.succeed("mount /data_fs /mnt")
+      machine.succeed("btrfs subvolume create /mnt/to_backup")
+      machine.succeed("mkdir -p /mnt/btrbk/local")
+
+      # The service should not have any triggering timer.
+      unit = machine.get_unit_info('btrbk-local.service')
+      assert "TriggeredBy" not in unit
+
+      # Manually starting the service should still work.
+      machine.succeed("echo foo > /mnt/to_backup/bar")
+      machine.start_job("btrbk-local.service")
+      machine.wait_until_succeeds("cat /mnt/btrbk/local/*/bar | grep foo")
+    '';
+  })