At that time; then.
introduces a comparison, and is associated with comparatives, and with words such as more, less, and fewer. Typically, it seeks to measure the force of an adjective or similar description between two predicates.
Used in comparisons, to introduce the basis of comparison.
At some time in the past; formerly, once upon a time.
At some time in the past; former, sometime.
During the same time that; while.
Up to the time that; till, until.