AWS Instance scheduler not working as expected

Hi everyone,

I'm trying to optimize our EC2 usage using AWS Instance Scheduler. Our EC2 usage is monday to friday, from 07:50 to 19:00 for which I have a working Instance Scheduler configuration that I'd like to fine-tune.

The goal is to avoid fixed bank holidays through the year, hence I was trying to apply multiple periods to a schedule, where each period models a month: a schedule s-office-hours with two periods office-hours-apr, office-hours-mayas shown below.

Schedule s-office-hours

scheduler-cli describe-schedules 		-s Instance-Scheduler --name "s-office-hours" 
{
   "Schedules": [
      {
         "UseMaintenanceWindow": false,
         "StopNewInstances": true,
         "UseMetrics": false,
         "Hibernate": false,
         "Timezone": "Europe/Rome",
         "Enforced": false,
         "RetainRunning": false,
         "Periods": [
            "office-hours-apr",
            "office-hours-may"
         ],
         "Name": "s-office-hours",
         "Type": "schedule"
      }
   ]
}

Periods office-hours-apr

scheduler-cli describe-periods -s Instance-Scheduler --name office-hours-apr
{
   "Periods": [
      {
         "Begintime": "07:50",
         "Monthdays": [
            "26-30",
            "1-24"
         ],
         "Months": [
            "4"
         ],
         "Endtime": "19:00",
         "Weekdays": [
            "mon-fri"
         ],
         "Name": "office-hours-apr",
         "Type": "period"
      }
   ]
}

Period office-hours-may

scheduler-cli describe-periods -s Instance-Scheduler --name office-hours-may
{
   "Periods": [
      {
         "Begintime": "07:50",
         "Monthdays": [
            "2-3",
            "5-31"
         ],
         "Months": [
            "5"
         ],
         "Endtime": "19:00",
         "Weekdays": [
            "mon-fri"
         ],
         "Name": "office-hours-may",
         "Type": "period"
      }
   ]
}

For some reason this configuration makes the scheduler not to work at all.

What I was able to retrieve from cloudwatch logs is the following message

WARNING : Skipping instance EC2:i-xxxx (debug-scheduler) in region eu-north-1 for account 1234567, schedule name "s-office-hours" is unknown

Where actually "s-office-hours" exists and is not mispelled anywhere (not even in EC2 tags)

I've googled a bit, and this message is shown when endtime comes before starttime, which does not apply to my case.

I suspect that could be smth related to conditions over Weekdays and Monthdays.

Can anyone help on this?