Oh, please don’t apply if it’s not a real application for the posted sit dates. As others have said, the system locks at 5 applications. As a HO, this action was super annoying to me! As a sitter, you may be robbing me of the opportunity to do the posted sit!! That HO may not reopen the process so a 5th, available person can apply.
The better thing to do is “favorite” their listing. The HO will get an email letting them know you like their listing. As a HO, I did find future sitters this way! You will also get a notification when any of your favorite listings posts new dates.