I have been teaching for 7 years and find that 2 hours is ideal. Take a morning lesson then break for lunch. After lunch spend the afternoon practicing. If you can, take a day off then come back for the second session.
Agreed, if you can split the days and practice in between it will help you grow and tweak things as you go. The lessons I took were group lessons for 2.5 hrs a week for 6 weeks. It was nice as there was plenty of time to practice, and being in a group we were able to progress together and learn from each others mistakes - and also laugh at each other's falls