So it appears that the only textual evidence on the Battle of Hastings was from Titania in CD:
"I have not exchanged words with my sister since before Hastings."
The rest is based on a few indirect WOJs that the fans have pieced together, well summarized by Serack
here.
Obviously the timeline is no place for fan theories. However, the Battle of Hastings did happen on 14 October 1066, the last time Mab and Titania spoke was "before" that, and a number of WoJs indicate that several major events happened at approximately that time (Mother Winter losing her walking stick, Mab's ascension to Winter Queen, Winter's ascension to being the guardian of the gates). None of these can be locked to the exact date yet, but perhaps this is enough evidence to at least put in a mention for future reference.