Yeah, I have tried to extend the timeout counter as far as possible, but it still times out after a while. I usually write replies in a sticky, then copy and paste when I'm done (when giving feedback on multiple mixes, listening to each in between, for instance.)
I haven't seen any way to add a 'save draft' type feature, but I'll look around again, maybe it can be done...(I'm not a programmer, my ability to extend the smf software is pretty limited, and I don't want to go to far from the stock version, as security updates still come out occasionally!)