At one time and Back when

At one time adverb - At a previous time.

Back when and at one time are semantically related in earlier topic. In some cases you can use "Back when" instead an adverb phrase "At one time", when it comes to topics like in the past, previously in time or order.

At one time and back when are semantically related in earlier topic. Sometimes you can use "At one time" instead an adverb phrase "Back when", if it concerns topics such as in the past, previously in time or order.