I've prefilled syringes for a day or two when I go on a backpacking (or other) trip.
I use a rubber syringe "stopper" or "plug" and attach a sterile pin when I'm ready to use it.

Using the plug keeps the profile of the syringe smaller (easier to carry), prevents air from getting in and oil getting out via the needle(due to elevation changes), and helps to keep the plunger from accidentally being depressed.

To hedge against external contaminants and potential leaks I put the syringe in a snack size zip lock bag with most of the air squeezed out.

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http://www.alibaba.com/showroom/syringe-plugs.html

I was told that if the oil is in the syringe for a long time that the black rubber plungers can begin to break down and tiny chunks of rubber can be floating in the oil... Not exactly a good thing

I never store the loaded pins. Any lil microbe has a chance to grow as time passes. Doesnt need to grow in the oil...the pin penetrates teh muscle as well.

If you will be to busy to take a whole 30 seconds to draw a dose how are you going to have time to inject?

I have loaded my syringes for a whole cycle in advance, never had any issue, one day is for sure OK bro

Syringes are made for injecting not storing, The oils will start to degrade the rubber stopper and plastics. Hens you will be injecting them. No more than 24 hours.

I don't know how long gear will last pre loaded in a syringe but I pre load a couple weeks worth at a time while running a cycle. I know for sure a day won't hurt anything at all. Oils have perservitives in them to help protect bacteria from afecting them.