I must be staying at different hotels than everyone else. I always put a DND sign up. Otherwise, housekeeping starts around 8 am (M-F) and 9 am on the weekends and holidays. They will get to everyone before 2:30 pm IME.
As for early check-ins, that might conflict with late checkouts if there are a lot of elite guests or if there are a lot of people checking out (since a new room requires more effort to clean than for someone who is staying another night).