Pick out some competitions in your area (www.robotevents.com) and design your schedule backwards from those (or better yet, have the kids design their schedules backwards from those). So at T minus X days the robot and program are done and only auton/driving practice happens, T minus Y days the design for the upcoming tournament is finalized, T minus Z days the game has been analyzed (or lessons from previous tournament have been learned and discussed), etc.
Basically, help the kids come up with a list of development milestones and put them on the calendar working backwards from each tournament. It will also help you help them stay on task, too. If a student is goofing off, you can ask “have you reached [next milestone, that I got you to set for yourself] yet? [If no] Is what you’re doing getting you closer to your goal?” rather than having to directly admonish them to stop hacksawing their water bottle in half (or similar).
As for how long each milestone takes, that will depend a lot on the students of a particular team as well as the availability of facilities/build time/etc. After a tournament, help them with a retrospective on their previous milestone performance as they go to lay out their milestones for the next development cycle.
As your students get experience, the job gets easier as they start being able to do a lot of this planning for themselves. Hopefully this helps, and good luck this year!