Wake up between sleep cycles at the right time.
Waking at the end of a cycle, when sleep is lightest, feels dramatically better than being pulled out of deep sleep mid-cycle. Multiplying cycle length by the number of cycles and adding it to the time you actually fall asleep gives the boundary to aim for; the following boundary is shown in case you would rather have the extra cycle than the earlier start.
Cycle-aligned wake time
Wake time = time you fall asleep + cycles x cycle length; next boundary = wake time + one more cycle
These figures are estimates based on population-average formulas and are intended for training and recreational planning only. They are not medical advice. Consult a qualified health professional before starting or changing an exercise programme, particularly if you have an existing medical condition.
Because you woke mid-cycle, most likely out of deep sleep. Sleep inertia after a badly timed alarm can outweigh the benefit of the extra twenty minutes.
It is an average. Cycles vary between people and lengthen through the night, so treat the boundaries as approximate targets rather than exact times.
Wake-window alarms attempt the same thing by detecting light sleep. They are imperfect but avoid the need to predict cycle length yourself.