In my experience, there's about a 1 in 3 chance that you'll be in for a *very* long wait. Attendant might have run to the dining car, or might be covering the adjacent transition sleeper, or might be napping, or...
I find it very helpful when they tell me where to find them, so that if something comes up, I know where to look rather than just pushing the button and wondering whether I'll hear back in a minute or in an hour.
I recall one occasion where I made up the beds for the people in the roomette across the aisle because the attendant was nowhere to be found. She turned up an hour later wondering if we still needed her.