The track is usually not open for public driving between the end of November and the middle of March. April, May, October and November are what we call the low-season months. The traffic is usually less but we also anticipate the weather not being favourable. That being said, if you are not afraid of a (semi-)wet track, these are the best months to come out. June to September are the high-season months. The area is thriving, restaurant seats or hotel rooms need to be pre-booked and the car park at the entrance of 'Ring is usually cramped. The experience is completely different, but the Nürburgring is the same, so it's up to you what you deem important and what your goal is for your trip.