at a time

English

In a single, continuous period of time.
He manages to abstain from smoking for weeks at a time, but then gives in and starts again.
Simultaneously at each occurrence (of some action).
climb stairs two at a time
- 1897 December (indicated as 1898), Winston Churchill, chapter IV, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd., →OCLC, pages 58–59:
  The Celebrity, by arts unknown, induced Mrs. Judge Short and two other ladies to call at Mohair on a certain afternoon when Mr. Cooke was trying a trotter on the track. […] Their example was followed by others at a time when the master of Mohair was superintending in person the docking of some two-year-olds, and equally invisible.

(in a single, continuous period of time): in a row, at a stretch
(simultaneously at each occurrence): at once, at one time, at the same time, simultaneously, together; see also Thesaurus:simultaneously

(antonym(s) of “simultaneously at each occurrence”): individually, one at a time, piecemeal, separately, severally, singly

in a continuous period

simultaneously