There are 210 sleeps (210 days) until May 21 (Friday, May 21, 2027).
There are 210 days until May 21 (Friday, May 21, 2027) — one sleep per night.
One sleep per night between now and the big day — tonight is the first sleep, and the morning after the last sleep is May 21. Sleeps are the same as days.
210 sleeps is 30 weeks.