That delay you talking about depend on how often you get new mail on particular account as gmail trying to not check account every minute if it's only get mail

That delay you talking about depend on how often you get new mail on particular account as gmail trying to not check account every minute if it's only get mail once a week. Though delay can be really low if you get new mail every few minutes. And you can artificially decrease it by setting simple script that would send some random mail to that account and then just filter it on gmail-side.