This query should show you the system maintenance status and time properties:

   SELECT * FROM prop.propertyentries WHERE category = 'SiteConfig' AND name ilike 'systemMaintenance%';

I suspect the values in the database are correct. It looks like the code that saves the system maintenance settings does not correctly detect changes to the interval properties and, therefore, doesn't reset the timer after interval changes. I'll fix this for 10.3, but in the mean time you can either 1) restart your server or 2) change the system maintenance time property to force a timer reset.

Sorry for the inconvenience...

Adam