This specific checkout error only fires when your Show End Time on Catering Ordering setting (Catering Settings, Catering tab) is turned on and the cart has catering meals in it. When that's the case, checkout requires both an End Time and an Event Time to be set for each day with catering items, and it also rejects an event time that's already in the past relative to "now." If "Show End Time on Catering Ordering" is off, this particular validation doesn't run at all.