Lifespan of Optimara 14-12-14 after mixed?

The title about sums it up...

I received a bunch of leaves and small plants several months ago from a member here in trade and am starting to realize that my initial fert schedule and source were not sufficient/appropriate.

Now I've got some Optimara AV Food sitting in front of me but I don't need nearly a gallon to water my teeny tiny plants :) Yes, I could just guestimate and mix a smaller batch but I was curious if any of you mix a whole gallon at a time while using less. I could probably use up the gallon withing about 10 days. Is this alright or should I just mix what I need per feeding?

Thanks in advance for any help you might provide.

You can always mix water and fertilizer anytime and save it. It won't make a bit of difference. I let my water stand overnight anyway before I use it on plants. Maybe it takes some of the chlorine out of the water.........anyway my plants look better since I started using 1 day old water from the kitchen sink

I always make up a gallon at a time and it takes me about a month to use it up. No problem there.