diff --git a/nixos/modules/services/misc/nix-optimise.nix b/nixos/modules/services/misc/nix-optimise.nix
index f3724a5a78cfa8..b9b10a4ef757ba 100644
--- a/nixos/modules/services/misc/nix-optimise.nix
+++ b/nixos/modules/services/misc/nix-optimise.nix
@@ -14,8 +14,9 @@ in
       };
 
       dates = lib.mkOption {
-        default = ["03:45"];
-        type = with lib.types; listOf str;
+        default = "03:45";
+        type = with lib.types; either singleLineStr (listOf singleLineStr);
+        example = "weekly";
         description = ''
           Specification (in the format described by
           {manpage}`systemd.time(7)`) of the time at