About waking at 7:15 AM
Quarter past seven is a fifteen-minute reprieve on a seven o'clock start that still leaves a working morning intact. It is also a common second alarm for people who set an earlier one they do not really mean.
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.