For work, email replies were expected within 48 hours, or at least confirmation of receiving the email and an estimate of how long you needed to get whatever the request was done. DMs were expected to be answered within an hour because nobody DMed unless it was important to get a fast answer.

Personally I try not to let emails go more than 2 days. People seem to DM about anything these days, so I’ll read it and based on what it is (and who it’s from) decide when to reply.