The next PPL ground school that we will be offering will be an accelerated program which will consist of two full weekends and an additional Saturday. Keep checking back for more details.
You don't have to start at the beginning, but jumping in at the start of a new topic would be useful. If you miss a class, you can catch up on it the next time around. If there's a section of material that needs some reinforcement or review, as long as you are a MFC graduate and did your initial ground school at MFC, you are welcome to sit in on any class a second or third time.
Also, you don't have to complete ground school before your flight training starts. In fact, most students have found that flight training concurrently with ground school helps reinforce the classroom concepts.