About waking at 7:30 AM
Half seven is the standard for a nine-to-five with a short commute. It allows about ninety minutes from waking to arriving, which is roughly what most people need to be genuinely alert on arrival rather than merely present.
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.