YouTube End Tmes not being respected in embed or markdown

First issue.  Squarespace doesn't appear to allow start times when adding video from YouTube when adding as media block (see photo).  (youtu.be/MrlVpbQeE94?si=z7T3IdKedQqu-aO5&t=17 (https://) left off on purpose.)

Second issue:  When embedding the video, the start time works just fine, but the end time does not.  How can I get it to respect the end time and stop the video?  Thanks in advance.

<iframe width="560" height="315" src="https://www.youtube.com/embed/MrlVpbQeE94?si=-qMxQKRv-AKNqD8w&amp;start=8;end=45" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>