Glad you're enjoying the Temporal API! Yes, you should be able to chain add({ weeks: n }) to move forward or back that number of weeks. Although I'd probably want to put the add before the startOfDay() call, because there's no guarantee (thanks DST!) that the start of a day is the same time on different days.

Also, if you just need dates and don't care about times, then you can use Temporal.PlainDate. This would also remove the need to worry about startOfDay.