Thanks sidjohn1 and Tony for the suggestions.
sidjohn - that definitely looks like a useful DTH and I’ll double check, however I think the issue is more how to send the info to the device rather than what it supports.
I managed to find out that if I select the button on the device which makes it run for say 30 minutes then run a CommandScheduleReport I get a valid response showing the schedule has been set. However I have my suspicion ST hasn’t properly implemented the schedule command class - the response I get is:
command: 5305, payload: 01 00 FF 30 00 00 1F 3F 00 78 00 01 03 25 01 FF
ST parses this as:
CommandScheduleReport(startMinute: 63, reportsToFollow: 0, scheduleId: 1, userIdentifier: 0, startWeekday: 0, reserved371: 0, durationByte: 120, numberOfCmdToFollow: 1, startDayOfMonth: 0, reserved241: 0, startYear: 255, activeId: 3, res51: false, startHour: 31, durationType: 0, startMonth: 0)
Which I think has a couple of errors but most notably does nothing with the last three bytes (25 01 FF) which is exactly the command I need to send!
@Tony - I did think of that, however you get the error that the payload is read-only (I think it is constructed by ST from the various properties).