at any one time—on each separate occasion:
- These were what were known as “bottle shops,” and could not sell less than a bottle of spirits at any one time.
at any time—
1. at any given moment:
- The navigational system enabled our bombers to know exactly where they were at any time en route to Germany.
2. at a time which may be very soon:
- We may need the trucks at any time. I’ll phone if I want you to roll them.
3. at any time one chooses:
- Anyone is welcome to join in at any time during the day.
4. no matter when; whenever:
- If at any time you have questions, please feel free to call.
See also: at all hours / at any hour.