There doesn't seem to be one and I use both cron (which has a tag) and 'at' at different times. I'm not able to add a tag at this time.
Tags just for more common commands would be very helpful. I would be able to help people with 'nedit' but no other editors, or 'alpine' but not other email interfaces.
atdis ~14... This query looks legit enough, 23 results and 7 out the first 10 could legitimately be tagged with it. The only thing I'd like to add is that as Dan remarks in the comments under Thomas. W's answer currently those are completely unbrowseable due to the overwhelming number of posts containing the preposition "at". Something to think about before deciding.
atis one of those commands that when I Google it, I really don't get relevant results because
atis one of those common words and Google might even filter it out when forming a query. I never would have thought to look for the tag 'schedule'.