Check if it's within 22 hours, and use "today" if that's the case - otherwise use from():
moment() < moment('2014-05-14 13:00:00').add('hours', 22) ? 'today' : moment('2014-05-14 13:00:00').from(moment());
"a day ago"
moment() < moment('2014-05-15 13:00:00').add('hours', 22) ? 'today' : moment('2014-05-15 13:00:00').from(moment());
"today"