Yes, depending on the guest, and how nicely they ask, it can be irritating.
Nonetheless, if they ask nicely, we're always happy to try to accommodate guest schedules.
It's usually an early flight or late flight (or both) that compels them to ask. If we have the availability and it's not extra work, we don't mind, and don't ask for additional compensation (again, depending on the guest's attitude). But sometimes, we just can't accommodate their odd schedule, so I'll tell them. Nicely.
And not to be repetitive (again), but things like this go a long way towards receiving glowing reviews. Well, from reasonable guests, anyway.