I install it add some permissions and my server removes from modded, i have to uninstall the plugin and reinstall umod and restart the server if i try. Anything you can suggest please?

It isn’t from this plugin. All of the plugins on our site have no control of where your server is listed, nor does the server list know which you are running.

I meant once I add TimedPermissions.cs to my plugins the server quickly disappears from the modded list and is no longer locatable on any list. It's literally only when I add this plugin, i have no problems with it appearing otherwise.

Installing this or any plugin will not cause your server to be unlisted, they have no control over that; especially this one. This plugin uses basic timers and universal API that Oxide provides, it does not change or in any way modify how Steam talks to your server.