Not sure if you can make this work for your use case?
I have my phone check every night at 9pm if I’m scheduled to work the next day on Google calendar. If so it turns on my alarm for the next day for me automatically. It has been working pretty reliable for a while now.
To accomplish this I use Tasker, gentle alarm, and a calendar plugin for Tasker.
It’s kinda the long way around to your goal. Possibly you could set your work schedule in a Google calendar, have it checked like I do the night before. If true set a virtual switch via sharptools that completes logic to fire your thermostat at your preferred time via Tasker or Core or Webcore?
Also maybe you could use the Gcal smart app to set a contact based on your work schedule in Google calendar. Then use core or Webcore to fire your thermostat to on if the Gcal app contact is true at the time the furnace should start to warm things up for you.
I haven’t tried or tested these ideas. Just tossing them out there for you to ponder on.