The USB-MIDI jitter under Windows 10 was up around 7ms for me (multiple computers, multiple interfaces, always the same result). XP was pretty decent, 10 is at least as good as XP, around 2ms total for me IIRC. Still loose but usually OK for sending transport messages and stuff.
I finally got a mioXL earlier this year, though, and switching to RTP-MIDI brought the jitter down to around .2ms, though, which is comparable to good hardware clocks and really about the best you can expect from MIDI. So that's the way to go if you use hardware but absolutely must sync to or sequence in a DAW and need tight timing. At least until MIDI 2.0 is actually a viable option, since I'm pretty sure it includes event timestamps that would make all of the issues with USB irrelevant.