This is the way most of the systems where I work function.

The timer turns the heat on when you expect to need it and saves energy the rest of the time. Usually it starts warming the place up an hour or so before people arrive or will use it. Some of our smart systems have an outdoor temperature sensor and an algorithm that learns how fast this building warms up.

The thermostat overrides this and turns the heat on any time the temperature gets low enough to be hazardous - break pipes etc.

It seems perfectly reasonable to me. You might be traveling during a hard freeze and come home to a house full of damage if the timer was the only thing controlling.