nix: do not optimise store on build, but regularly

hosts/common/global/nix.nix

@@ -2,7 +2,8 @@
   lib,
   outputs,
   ...
-}: {
+}:
+{
   # Apply overlays
   nixpkgs = {
     # TODO: apply this to hm and nixos without duplicate code
@@ -18,7 +19,9 @@
     };
   };
 
-  nix.settings.auto-optimise-store = lib.mkDefault true;
+  # optimize at every build, slows down builds
+  # better to do optimise.automatic for regular optimising
+  # nix.settings.auto-optimise-store = lib.mkDefault true;
   nix.settings.experimental-features = [
     "nix-command"
     "flakes"
@@ -32,6 +35,10 @@
     # Keep the last 3 generations
     options = "--delete-older-than +3";
   };
+  nix.optimise = {
+    automatic = true;
+    dates = [ "weekly" ]; # Optional; allows customizing optimisation schedule
+  };
 
   programs.nix-ld.enable = true;