I pump two times in the office, every 4 hours... I just put back the stuff in the box, and reuse in the second time.. I think the air-conditioning temp. is ok for such, as the milk is ok for storing up to 6-8 hours in such temp (below 25 C)
so far ok..... However, all depends on the environment.....it's really better to sterilize everytime you use.....
I also get some chu chu sterilizing bags (in microwave) in the office..... during July/Aug, I washed them and used this bag to sterilize as I think the weather was too hot..... so it's better to sterilize each time...