The TimeMap is in fact loading the data from OpenHistoricalMap on the deep zoomlevels (streets) so if you edit OpenHistoricalMap roads and houses it will be displayed there.

See Lille for example - and play with timeline here:

https://www.oldmapsonline.org/en/history/regions#position=13...

You will see directly how the town center has developed, fortifications, railways or highway... damn cool! :-)

I don't see mention of OHM anywhere within TimeMap, is there something I'm missing? Is there a page about where the historical data comes from for the map?

I love OHM! Some places are impressively well-mapped, for example NYC.