There is no requirement for contact per ebay's rules. However, that is odd for so much time to have gone by. Did you message the seller on a week day?
I know it is frustrating, but not every seller is the same in terms of how they sell and how communicative they are. If a seller states a 10 day handling time, that would sum it up for me though, lol! They will probably get back to you in a day or two - even if it has been a day.