From my experience, while working on a software development team and replying all the time to questions from testers, business owners, managers, etc., I think I

From my experience, while working on a software development team and replying all the time to questions from testers, business owners, managers, etc., I think I would sum it up like wheels did: as soon as possible, even if you don't know the answer. People will appreciate the consideration. There are cases when may not have the time to reply immediately to all questions (e.g. small team). In that situation common sense will tell you which ones are more pressing, I guess. Going a little off topic, one thing I've been noticing that works pretty well (especially in agile environments), if you can afford it time-wise of course, is to have one person exclusively dedicated to support for a week. Then rotate to another person next week. That will both keep the requesters happy to get answers on time, but also the repliers, who can fully focus on other things when they are not "support person of the week".