Ancestry posted "The Ancestry.com website will undergo scheduled maintenance on Monday, 21 October, from approximately 10:00 a.m. to 1:00 p.m. (EDT). During that time, some portions of the site may be unavailable. Thank you for your patience."
This message first appeared AFTER 10AM (EDT) this morning, so I'm going to guess this was not scheduled at all, but due to lots of weekend wonkiness.
Picking and choosing sync times requires a crystal ball. The site has been so buggy of late, there's never a good time to sync.