Just buy a 240v DPST 24 hr mechanical time switch and wire it into the electric furnace circuit (or furnace fan circuit if you have a gas-fired furnace). Interm

Just buy a 240v DPST 24 hr mechanical time switch and wire it into the electric furnace circuit (or furnace fan circuit if you have a gas-fired furnace). Intermatic makes them. The ‘smart’ thermostat can call for heat all it wants, but nothing will happen if the time switch relay contacts are open. I’ve seen 50 year old 24 hour mechanical time switches operating just fine, and you won’t need to replace your thermostat. This one is $122 and comes inside a NEMA 1 enclosure: https://www.intermatic.com/Product/T104?setcontextlanguagecode=en https://www.intermatic.com/Product/T104?setcontextlanguageco...