I'm still very uncomfortable with the loop approach. It's just going to be slow. But, you need to make sure that each command is a single transaction, or, the entire set will wait until you're done through the whole loop to commit. So explicitly start and commit the transaction around the command to do the insert.

Also, instead of capturing start & stop time in the code (unless you're trying to measure the code itself) instead use Extended Events to capture the execution times of the commands.

I still don't completely understand what you're trying to do or why it has to be done in a loop.

Here's an article differentiating the set-based operation.