The split serves the schedule
Two full-body days, three full-body days and four upper/lower days are organizational options. They are not ranks of seriousness. Start with the schedule you can repeat and the movements you can perform with control.
Rest is part of the session
Budget time for warm-up, setup, working sets and pauses. Rest between sets changes the pace and quality of later work; rushing a difficult set to satisfy an arbitrary timer can make the comparison less useful.
Review the pattern, not one day
A single session can be affected by sleep, stress and unfamiliar equipment. Look for repeated patterns in your log. If the same movement repeatedly deteriorates, review the load and setup before adding more work.