https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/alarms/create

On Chrome, unless the extension is loaded unpackaged, alarms it creates are not allowed to fire more than once per minute. If an extension tries to set delayInMinutes to a value < 1, or when to a value < 1 minute in the future, then the alarm will fire after 1 minute. If an extension tries to set periodInMinutes to a value < 1, then the alarm will fire every minute.

Chrome 120: Starting in Chrome 120, the minimum alarm interval has been reduced from 1 minute to 30 seconds. For an alarm to trigger in 30 seconds, set periodInMinutes: 0.5.

This appears to also be true for when and delayInMinutes