You don't get weeks back, you can't trade them for smokes, or pudding/fruit cups. It's not jail man it's growing weed lol.
Like most people have said and will say forget about this 'its a 9-10 week strain' business. It's weed. It'll be done when its done. Be it 9,10,11,12+ weeks. It finishes when it finishes. Just keep growing and harvest it when it's finished. Forget the days hours and minutes. It's 90% useless Information unless it's a strain you run on a regular basis from cuttings of a single mother, and even then there's factors that will slightly change the ripening time every run. It's just an idea of when to be looking closer to determine the time YOU want to harvest based on personal preferences or needs.