""So it's definitely not recommended wearing it at night" - this is 100% added speculation". Haha. Please relax, this is rather my personal recommendation.
Unfortunately you never know when it's highest or lowest or whatever, there's no any visible indication of that on the watch. They recommend holding it 10mm from your head to avoid reaching tested levels.....you're absolutely right!
The FCC limit for public exposure from cellular telephones is an SAR level of 1.6 watts per kilogram (1.6 W/kg), for 30 minutes if exposure. Apple Watch levels are exactly that.