By using plastic bottles, you can tell quite easily whether they are carbonating ok or not, just by giving them a little squeeze
Just like a bottle of pop, if they are carbonating well, obviously the pressure in the bottle builds up, and the bottle feels very hard! Otherwise, it feels soft, and you can easily press it in with your hands. When I bottle mine, it can take between 2-3 days before they feel like they are fully carbonated, and on more than one occasion I have thought that it hadn't worked, but keep the faith, and all will be fine!!
Enjoy!!