I think you'll be okay if you make a starter a couple of days prior. I once bought a vial from my homebrew store, then ran a bunch of errands on an 85oF+ day. I kinda spaced out and forgot I had a vial of yeast in the trunk of my car!
Twelve hours later, I got it into the fridge. No harm; things went fine.
I agree with Dyer
; I'd go with something bigger than the mason jar, if at all possible. I use a 1/2 gallon growler that I got from a brewpub, much like the one shown below. Besides, it gives you a good excuse to go to a nearby brewpub! (Like I'd need one!)