Okay, yeah, so, that method was BS for two reasons: I'm formatting the milliseconds from the log record, but the rest of the timestamp from "now" (lol, ouch) – but also, the underlying problem is using time.strftime (like the base class) instead of the more modern datetime.datetime.strftime. Because the latter actually _does_ have a format string placeholder for microseconds (not milliseconds though).
So, after a bit of iteration, I think I'll be going with this one: