Student or Learner
Can I use "at that time" and "at the time" interchangeably?
Can "at that time" refer also to future?
"At that time" can be used for the future; but it can't always replace "at the time".
1. At the time that I first knew Miss X, I had just finished a long relationship with Miss Y.
— here, "at that time" would sound odd.
2. It was at that time that I decided to become a nun.
— here, "at the time" would not be possible.
However, often, "at that time" would simply be a more emphatic version of "at the time".
All the best,
Not a professional ESL teacher.