Hmm, I've not had any issues with the Nest starting up the HVAC at the wrong time. Make sure the "Early-On" option is set to OFF? Also, on mine I have Auto-Schedule OFF, Cool to Dry OFF, and Airwave ON. And when I don't want the HVAC to run I use target temperatures beyond reasonable possibility of turning on in my house (e.g. cool to 80 degrees, or heat to 64 degrees).