When I add a YouTube URL with starting video timestamp in my forum post (e.g. https ://youtu.be/QAzE-_ocf1U?t=601 See example forum post here), the timestamp part (?t=601) is automatically removed by the forum software for some reason. I had to add extra comment in the post telling readers to go to mm:ss to watch the relevant segment. It would be better if readers can click on the timestamped YT link without having to do anything.

To help the [youtube] tag work, the site has code to "normalize" YouTube links to a common canonical format. But I see your point, if you're not using the [youtube] tag, the code modifies the link anyway. I will look into making it more discriminating.