Founder or just regular person, we all need time off from work. How much and when will vary by person and the requirements of the job.
As the “founder” of a solo freelance business I try to take weekends off but sometimes I have to get some work done.
Thus the reason of "founders" in the question.
But in general, dedicate 3 hours per day to anything except your work, it's more valuable than 21 hours during a weekend.