I came from Zwift a couple of years ago for SYSTM’s 4DP plans and vids, which are way better than Zwift for my purposes. About the only thing you can do with the plan calendar is choose the start day. The default is a Monday assuming a 5 day workweek starting on Mon and schedules longer and higher TSS rides on Sat-Sun. You can change the start day to something other than a Mon, say a Wed, then the longer workouts would fall on Mon and Tue. Otherwise, you can drag and drop workouts on the calendar as you see fit.