My oldest and I used to get into arguments about brewing times for tea. He worked for a coffeehouse, and knew the standard brewing times employees were told to use. I explained their brewed teas had added ingredients, therefore needed longer brewing times to be stronger, but that that didn't make it better.
Of course, I was right. ;)
Anyway, there are differing views on brewing times, but I have found these to be best:
Black and oolong teas - 3-5 minutes
Green teas - 1-3 minutes
Herbal teas - 5 minutes
You can always let your tea steep longer if you like it stronger, but I find oversteeping makes them bitter.
Green tea with lemon and ginseng.