Tommee Tippee Insulating Bottle Bags

Hi all, first time mum here and basically clueless. I bought the tommee tippee anti-colic complete feeding set that came with the insulated bottle bags. I plan to breastfeed but also want to pump so family and my partner can feed if I'm away. My question is do you have to warm breast milk? Home long does it keep when warmed, and can you use the insulated bags to keep them warm for more than a few hours?

So many questions I know but will be very grateful for any responses