Or maybe episodes don't take place the day they air. Fall Weather Friends came out about a month after Winter Wrapup

Commendable effort – but I really don’t think we can take air dates as canon dates. After all, that would mean that important stuff in Ponyville only takes place on Saturday. And we know that can’t be the case because we’ve seen school in session before, so at least some episodes were taking place on a weekday.