For me (on IRC) the rule was always that it's fine if people don't answer within 10 minutes, but you should be told. Specifically, you're expected to answer in

For me (on IRC) the rule was always that it's fine if people don't answer within 10 minutes, but you should be told. Specifically, you're expected to answer in IM timeframe unless you set an afk message. This way people know that they should wait for an answer that might not come until hours later. In an office this is self evident since if you walk to your colleague's desk you see if they aren't there, but requires a bit of explicit communication via IM. I simply set my status to "AFK deep code" or simply "afk" and turn off notifications to get 2 hours without interruptions when I need it