Hi Want2bwell, i also think 3 hour GTT minimum, the longer the better ..and you really don't want to let yourself get to the stage of feeling weak and shaky, it's better just have a small healthy snack in between meals to keep your blood sugars up to a good rate, even just a an apple or a pear [for example] in between main meals can help a lot and eating smaller portions at the main meal time puts less strain on your pancreas to produce enough insulin, its better for people with pre or diabetic condition to have 6 SMALL meals a day spread evenly during the day than the regular 3 large main ones.
A variety of high fibre/ low GI foods will release more slowly into your blood stream, they will keep you from feeling hungry for longer.

Brian