I'm pretty sure that those, and all the other items served up from the /ui folder, are delivered from the server to the client as static content (not processed server side).
They will contain code, which in turn can pull other resources, that may give the appearance on the client side of taking up time, but there should not be significant time spent from the point of view of the server, and the app-access logs can help to confirm that (the time for the server to deliver them in ms should be present for each request, and is the total time from receipt of the request until the last byte was sent back out again).