I spend almost 16 hours a day on my electronics so I want to set a timer that when it hits 0 I have to go full ascetic and lock up all my electronics. How long should the timer be? How much time to use electronics is enough for one day? 4 hours? 6 hours? 8 hours? 10?

>>106119001 (OP)
I don't think going from 16h->4h in one shot is realistic. Maybe set it to 12h first, and instead of a countdown timer maybe choose a few electronics-free hours throughout the day.
You need to find new activities, start doing them regularly, and let them naturally replace some of this time.

go full shabbos, that should answer most of your questions.

>>106119001 (OP)
just pick 2 weeks every 3 months and go full amish