第一个错了应该是at one time ,一度,从前.
如：At one time I used to go skiing every winter.我有一度每到冬天就去滑雪.
at the same time是同时的意思
如：She and I both arrived at the same time by pure coincidence. 我和她同时到达纯属巧合.

at the time在那时, 在那段时间；当时；旋
如：This was the wise decision at the time.这在当时是一个明智的决定.