@WJh 

Your fastest path would probably be to try to modify the time range afterwards using the Omada API and a script, and that's assuming they didn't hardcode the event scheduler on a 15min interval.

  @WJh 

It dawned on me that the latest API doc (5.4.6 from what I can see) wouldn't have the Time Profiles defined in it...so I did a little sleuthing for v5.8.4 controllers:

URL to set a Time ACL

HTTP 1.1 POST to your ControllerIP:PORT /{your_controller_id}/api/v2/sites/{your_site_id}/setting/profiles/timeranges 

For example

https://192.168.0.100:8043/{your_controller_id}/api/v2/sites/{your_site_id}/setting/profiles/timeranges 

Here's the JSON structure of the POST payload:

Text: 

 {"name":"test2","dayMode":0,"timeList":[{"dayType":0,"startTimeH":8,"startTimeM":0,"endTimeH":18,"endTimeM":0}],"dayMon":true,"dayTue":true,"dayWed":true,"dayThu":true,"dayFri":true,"daySat":true,"daySun":true}

  @WJh 

So things are looking pretty good for setting Time Profiles down to the 1-minute increment.

There are a number of Omada SDN script projects out there if you need further help to get started on the basic authentication to your controller.