Your app will show you the number of days until your next check-in, and this will automatically count down from day 28. This is the recommended amount of time to spend on each cycle.
Don't worry if you're not completing your plan in line with the countdown. When you reach 0 days, it just means that you can submit results and check-in from that point onwards. If you've not completed the cycle by this time, that's no problem. You can simply delay submitting results until you've smashed the cycle and feel ready to move on. This is your own journey.
Remember, you'll need to submit results and check-in at the end of each cycle to access your new workouts and recipes.