Turn-around time is usually 2 days, but sometimes you can get it back within a day. Check with your room steward.
There will be a blue cloth bag in one of the closets along with a check-off list. Stuff as much laundry as you can into the bag, fill out the check-off list and either leave it on the sofa or your bed at night before the steward makes up your room or in the morning when you leave for breakfast.
When we boarded, they were having a special flat rate for all your ironing for a flat fee (unpacking special?) (can't remember the price) and also for a laundry bag full of clothing for wash for (if I remember correctly)$20.
Had I known at the time of packing, I may not have folded so carefully!