After a set time, the mastodon interface will be covered by an overlay with a countdown.
When the countdown expires, you can click the overlay to get another dosis of masto-time.
When you first open the tab, it's configurable whether to start immemdiately or show the
expired overlay waiting for a click.
With some adjustments this could be adapted to any website.
Due to cross-origin policies, it's not possible (in the form of userscript) to track all your instances. This means each instance gets its own throttle timer. It works best when you have one primary instance where you go exclusively.
The unlocked time runs even if you close the tab. Keep that in mind. Closing the tab to "keep some minutes for later" won't work.
To make it run on your instance, add it as a new @match entry at the top