upd

info.nix

@@ -1,4 +1,7 @@
 {
   hostname = "nixos";
   username = "biscuit";
+  timezone = "America/Chicago";
+
+  vpn_enable = true;
 }

modules/system.nix

@@ -1,9 +1,9 @@
-{ ... }: {
+{vpn_enable, ...}: {
   imports = [
     ../system/bootloader.nix
     ../system/firewall.nix
     ../system/locale.nix
-    ../system/networking.nix
+    ../system/network.nix
     ../system/term.nix
     ../system/development.nix
     # ../system/proxy.nix
@@ -13,5 +13,6 @@
     # ../system/touchpad.nix
     ../system/users.nix
     ../system/tools.nix
+    (if vpn_enable then ../system/vpn.nix else null)
   ];
 }

system/timezone.nix

@@ -1,3 +1,3 @@
-{ ... }: {
+{timezone, ... }: {
-  time.timeZone = "America/Chicago";
+  time.timeZone = "${timezone}";
 }