Nobody expects you to drop anything. They want to see if you're there, and if you're not, they'll look for someone else to help them instead of asking you a question that might not be answered until long after they already received an answer from someone else.
If you don't want to interrupt your work and reply, then don't. Don't be rude and expect people to read a manual about how to interact with you.
> why Tim waits 4 minutes to reply to the "Hello!", but instantly replies to "Hello! <question>". What a selfrighteous jackass.
As far as I can tell, this question only makes sense if you expect him to treat both messages with equal priority, and believe failure to do so makes one a jackass. If you agree that it's reasonable to treat "pings" with lower priority than concrete questions, then it seems pretty easy to imagine why Tim waited 4 minutes to reply to "Hello" but instantly replied to a question.
Nobody expects you to drop anything. They want to see if you're there, and if you're not, they'll look for someone else to help them instead of asking you a question that might not be answered until long after they already received an answer from someone else.
If you don't want to interrupt your work and reply, then don't. Don't be rude and expect people to read a manual about how to interact with you.