My glop lasts a couple days (kept warm) if I push it, but one might as well pour tissues from all the glop one makes, and make fresh glop for more tissues. My attempts to keep glop in the refrigerator has resulted in smelly biological experiments. I make two or three batches of glop at a time (usually 850ml per batch). Each batch makes three 14x17 tissues.
I dry tissues on cardboard, stuck on with push pins. Once dry (two days in my climate) I just stack the cardboard and use as needed -- usually within a couple months. The push pins keep the surfaces of the tissues from touching anything. They all print fine, but I do notice that the fresher the tissue, the easier the non-exposed gelatin melts...but never to the extent that the gelatin is difficult to melt.
If one's climate is dry, then one might have some problems with the tissue curling and/or cracking. But with a RH of 60 to 70%, that is not a problem here. So Andrew's suggestion of bagging the tissue would be good in areas of low RH.