In terms of a driver's career or video game career lengths?
Keep in mind this isn't a type of game that warrants itself to the type of 'manager' user who would typically sim sessions or games. So you should and most will be taking part in every race weekend. That's FP1, FP2, FP3, Q1,2,3 (if you make through) and the race. If you choose 100% length weekends that would make a season take a seriously long time.
That being said I can understand your hesitation with a Codemasters release. However their approach this year seems much improved. They had a 3 stage beta with some 300 users and have approached the community well before release for feedback. I'm hoping that many of those release date bugs have been squashed already.