Each logical “page” overlaid upon the homepage is responsible for initializing the time slider control. We’ve been swizzling each page’s page loading code so that the time slider loads asynchronously before the rest of the page loads asynchronously. The swizzling has been responsible for several bad merges causing serious regressions (see for example #1044 #1104).

As far as I can tell, the time slider initialization code no longer needs to run asynchronously, thanks to changes to how the map loads in OpenHistoricalMap/ohm-website#316. We should restore the upstream page loading code and simplify time slider initialization to work like any other control that gets added to the map.