Hi, I have heard and read that Caninsulin is only really 'valid' for 28 days after opening. Is this really the case or is there some wiggle room with this? I only ask as I am on my second bottle now and the 28 days are up on 19th September, yet I still have nearly half a bottle left. Seems such a waste but understand that if the potency of the insulin starts to decline after 28 days ...but just wondering if 28 days is the set number. The vet is currently prescribing me 40ml bottle. Thanks!