I work for a vet and once the vaccine has been mixed it must be used within 30 minutes. I have heard of people using them after being mixed for longer periods of time, but considering the possible outcome and the fact that the vax aren't that expensive, you have to ask yourself if it is worth the risk.
Thank you! No, its not worth the risk! I was just curious about it because Ive never run into this scenario. I will buy a new one for my pup, and throw this one away. Thanks again!