MQ Gas sensors - can heater coil be run 24/7?
I have used the MQ-6  extensively. It takes minutes to warm up to get a stable reading. My experience is that if you stay within the voltage specifications for this device it will last 2-3 years before it burns out.

If you only need a reading every hour the approach of powering it up for a few minutes and taking a reading will make it last much longer.