D.W.
I found conflicting information by doing a quick google search as it's been a few years since I nursed.
Breast milk needs to be used within 24-48 hours after being pumped if in the refrigerator according to breastisbest.com (http://www.breastisbest.com/infofreezingbreastmilk.html)
It's not worth the possibility of bacterial growth after that point in my opinion. Though, I'm sure we froze/used breast milk up to 3 days after pumping.
You will become very engorged if you're used to expressing your milk many times during the day when you're gone, and it will affect your supply because you are dramatically reducing your demand.
My advice, take your pump, get a locker at the bus station to store it while you're walking around and pump in the morning/afternoon either on the bus or when you arrive at the station in the bathroom.
I had to travel multiple times while travelling for business, and I've pumped in many airport bathrooms. it stinks, but if it's important to nurse your child, you'll figure it out. You can also get a hand pump which is much smaller and store it in your purse (though it takes longer). I'd recommend dumping whatever you pump as you won't be able to keep it cold.
I've had to pump and dump several times - I know you're flushing precious breast milk down the drain, but it was more important to keep the production up.
Here's what the American Academy of Pediatrics has to say about breastfeeding as well (there are several pages of articles):
http://www.healthychildren.org/English/ages-stages/baby/b...
Good luck. Enjoy the day if you can.