About waking at 10:00 PM
Ten is a bedtime alarm for anyone getting up between five and six. Working back from your wake time in ninety-minute sleep cycles is a more useful way to choose a bedtime than picking a round number and hoping.
Leave the tab open
A browser alarm can only ring while its page is open. It does not have to be the tab you are looking at, and on a desktop it does not have to be the window in front — but closing the tab or quitting the browser stops it. For anything you genuinely cannot miss, set a second alarm on your phone as a backup. That is true of every browser-based alarm clock, not just this one.