About waking at 9:00 AM
Nine is a weekend alarm, a late-shift alarm, or a deliberate recovery lie-in. Keeping weekend wake times within about an hour of weekdays is the single most effective thing you can do for sleep quality, so nine works best if your weekday alarm is around eight.
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.