There are 199 sleeps (199 days) until May 10 (Monday, May 10, 2027).
There are 199 days until May 10 (Monday, May 10, 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 10. Sleeps are the same as days.
199 sleeps is 28 weeks and 3 sleeps.