I would reserve it for the 22nd and email/phone your hostel ahead of time advising them that you are going to be late. So they know NOT to give away your bed.
I have been to: Myanmar, Laos, Cambodia, Thailand, Vietnam, Singapore, New Zealand , Australia, Fiji, Costa Rica, United States, England, Ireland, Wales, Northern Ireland, Scotland , France, Italy, Switzerland, Germany, Austria, Vatican, Guatemala, Belize, Honduras, Nicaragua, El Salvador, Panama, Colombia, Mexico, India, Nepal.
Where to Next? Iceland!