Greasy Fork

Your timestampToSeconds will always return true. This will disable the next button.

You need to return false if parts.length < 2.

It's true if there's no text, like when you click the next button. This script will prevent YouTube from skipping to the next video.

Thanks, I haven't noticed this edge case as I have those buttons removed.
I've added this check. There shouldn't be any issues now.