Also, even tho there's a bump button for topics, I think that the bump option isn't available for all topics.
The bump button is not the only way to bump topics. For the rest you have to post something to bump it (but you have to be certain you don't bump too often though).
And explaining clearer your problem will always help you.
Of course, we could just answer "usually about 17-23 GMT" which may be completely wrong since the numbers change while certain regions gain or lose interest. And may not help you at all, since I see the bumping/clarifying option is used by most.