Momentarily in comments
I just got this on Android Enthusiasts:
Unless this has changed again (and to something that doesn't make sense), it should be "just now" instead of "momentarily".
It may be related to https://meta.stackexchange.com/questions/106297/momentarily-is-being-used-on-the-mobile-site-where-just-now-should-have-remai (see Tim Stone's comment) but this is the first time I've had this happen on the non-mobile site, and it was happening consistently on the mobile site.
As per the comment below, this doesn't happen consistently. I'm wondering if it's showing "just now" for 0 seconds, and "momentarily" for negative seconds. Negative seconds are much more rare due to how closely time is normally synced, which would explain why it's rarely seen.