I can't tell you how many times I've gone into restaurants in Italy at what I thought was dinner time only to find the place nearly empty. This is usually a good reason to leave a restaurant, because if the locals won't eat there, why should you? In Italy, however, you need to check the time before you make that judgement call.
Italians eat late - not as late as the Spanish, in most cases, but the dinner hour in many cities doesn't start until at least 8pm if not later (in Milan, restaurants don't get busy until 9pm, even on weeknights). Many restaurants in bigger cities and towns (especially if they're even relatively popular with tourists) will be open earlier than that, but the earlier opening time isn't for the locals. It's for visitors.
If you can't adjust your dinner hour to match that of the locals, that's fine - just remember that if a restaurant is dead quiet at 6:30 or 7 in the evening that may have nothing to do with the quality of the establishment and everything to do with the time.