I am interested in trying a wood gas stove for backpacking and wondered how long I could keep a fire going or at least hot coals, without doing any damage to the stove. Some cold nights before bed it would be nice to keep a warm cup on the stove or have some fire light. Would 2 hours do damage?

I dont think 2 hours will cause any problem. I have used my tin can stove to sit round after cooking and I did not time it but I would have thought it was that long. Corrosion and heat will destroy a stove eventually.