Sometimes I run into him 2 rooms in, at times it takes me a hour or so. Hints apply to a very broad group of rooms. Just think of exp and riches and beat as much trainers if you can.
If they point you to a lower floor and you want to be efficient, go to lowest floor possible, if they point you to a higher floor there, you can go the highest one not yet visited. Eventually you can round it down that they give you pointers like northeast or so. The gate trainer himself will point you to the floor the gate is in. And you can't really miss the gate if you look everywhere on the floor you need. Often you'll find the closed gate before the gate trainer.