When we eventually find a block, is the 5nd difficulty used the difficulty when we find the block, or the difficulty when we found the prior block, or something else?

For example, difficulty was 2.2T when we found the last block, and it is currently 2.6T, and probably rising to 2.8T soon.

There is a difficulty change coming up in about 34 hours.   https://diff.cryptothis.com/.