they want and for as many days as they want to. By policy, if a student is excused, a teacher is required to allow the student to make up any missed work. Now, it doesn't say that you have to give the same assignment/test/quiz. So, it could be harder than the original. Also, no grade is guaranteed. So, they could get a D- instead of that A.
When I taught, I didn't really care when they did the work. I cared if they did the work. So, I had students come in to me on the last day of a term and ask what they could do to get their grade up. I handed them a pile of work and told them to get it in ASAP. 9 times out 10 they just didn't do it but I wasn't the butthole rejecting them.