at a set time
Do we have to eat in this hotel at a set time , or may we come down whenever we want?
at a time
He jumped upon two stair at a time.
He ran up the steps two at a time.
at bay
They ran the thief into a house, and there the thief turned at bay.
at (the) best
We can't get to New York at ten o'clock at best.
The treasurer had at best been careless with the club's money, but most people thought he had been dishonest.
at call
The firemen in the town are at call if any fire should break out.
The dog was trained to come at call.
at close range
The police officer fired at the fleeing murder suspect at close range.
flee - fled
Night had fled.
The robbers fled when they saw the police.