Pre-covid...
For room service Continental breakfast you can hang the order form
(
https://disneycruiselineblog.com/menus/room-service-breakfast/)
with your selections on your door before you go to bed, checking off the 1/2 hr time slot you want it delivered and for us it's usually in the early part of that time. (We use it as a wake up call and quick breakfast on early port days.) For our after 10pm orders of cheese plate/fries/Mickey bars we've received those within 15 minutes on the Magic/Wonder...but there is no guarantee... depends on how many orders they get at once, how complicated your order is, and how many people they have making deliveries. Just remember to tip your delivery person--we usually do $1/item.