Generally as soon as lunch begins (I think 11) is the least busy time for counter service lunch. Dinner can be harder to get an un busy time as the restaurants are pretty busy from noon on. There is probably a slight lull around 4pm, but that's a bit early for dinner. We generally eat at 5pm, and we have to wait in lines, but the lines are noticeably worse around 6pm. If you like a late dinner after 7pm, then you're probably pretty good for shorter lines too.