Holberton is an intensive full-time program. Please, plan to dedicate 60+ hours a week to the program since great results are a product of committed hard work.
The first month, it will be mandatory to be onsite every weekday 9a-3p or, occasionally, 9a-5p. Past that point, you should expect 2-3 mandatory days a week that taper down as projects get more complex and deadlines are further out. Mandatory days are usually 9a-3p, with occasional 9a-5p days.