Slept on a flat rock just below the summit to stay out of the breeze (which died off after sunset), but we were well-prepared with winter gear (even though early September)...probably in the low 40’s overnight. Marcy alone in late February? No way in hell. (Climbed a number of the 46’ers, but never made it up Marcy...go figure.)
Algonquin has easier access, which is why so many people choose that over Marcy. It's a much shorter hike as well.