Earlier quoted context omitted.
On the other hand, there often needs to be a time limit, or else they will be too late to make an offer to the runner-up (when the leader turns it down). I am not sure what a 'reasonable period' is.
Long enough for you to wrap up your other interviews. I think the biggest issue is when the time limit isn’t moveable. If you’re finishing up interviews next week and the time limit cannot be moved, then that is a problem. Inflexibility from the get-go is a bad way to start a working relationship.
There is no reason to be nice or considerate to companies, they will drop you in hot second if it is convenient for them.