proposition is needed or not

Question

Hello, I want to know whether "at" is needed in the following sentence or not, let me know if the sentence needs a substitution for "at".

The pain at the site of surgery during both resting and swallowing was different at 6h, 12h, 18h, 24h, 36h, 48h, and 7d following surgery.

Answer 1

"At" would be used in this particular sentence. When it comes to the rules of preposition, one would use the word "at" in relation to specific time(s) or holidays/events.