jordi's dashboard

I am a researcher that can more or less decide my own schedule.
To assure I am not being lazy I put the goal of working 8 hours/day.
I have soon discovered that 8hours/day will be too strict if you really meant to work no more than 8 hours/day.
Whenever you read something more than one minute without interaction ( for instance trying to figure out what an equation means) or go to the bathroom 3 minutes, etc will not count as working hours.

Anyone has any rule of the thumb for how many hours should be the equivalent for 8hours/day