Hi @Jo86
If it doesn't inconvenience you to accommodate a late check-out, it truly is last minute, and no guests arriving that night, then I would consider NOT charging for one. It builds goodwill and is something that we do all the time - and guests thank us for it in the reviews they leave. We do it for both early and late check-outs.
If however guests ask for one in advance, where there's a chance we could sell the next night, then we simply ask them to book that night and all the charges will be taken care of.