I think this looks really cool. I like the ability to send multiple challenges to a candidate. I also like that as a side effect, it tests a candidates proficiency with Git.
I would choose a large time window- 4-8 hours or so. That way it ensures there is plenty of time to complete the challenge but also that it gets done in one day, like a normal workday.
I would choose a large time window- 4-8 hours or so. That way it ensures there is plenty of time to complete the challenge but also that it gets done in one day, like a normal workday.