Hi MMM, "sort of" is an expression used colloquially to make something sound more vague or if you are unsure of the exact date/time period that you are referring to. 1. So "sort of" means "kind of", or approximately, or thereabouts. 2. The sentence means that you are thinking back to a time when something happened but not to the exact time, rather to a moment in the past. 3. You can use this sentence to describe something that was a while ago, as you reflect or not. For example, "it was sort of at a time when people didn't use their mobile phones". So, in this instance, you are not giving the precise time, rather an approximation.

Natalia C gives a fantastic answer, but also be aware that 'sort of' and 'kind of' are sometimes used in speech as fillers, like 'um' or 'er'. So often, 'sort of' actually means nothing at all, and you can ignore it!

Kind of and sort of are very common expressions in speaking. They soften other words and phrases so that they do not appear too direct or exact. Kind of is more common in American English. Sort of is more common in British English: He's kind of jealous that they have become such good friends