I went back to work away from DD for two afternoons or mornings a week when she was about 8 mths old (she stayed with my gf). Since you'll be popping in at lunch you'll probably find it works quite well. I always bf her right before I left, ie where she was being cared for, and then as soon as I returned. She would go up to 5-6 hrs without me. I left a couple of bottles of EBM (frozen) for my gf, just in case. But only once did she even bother defrosting it because I was stuck in a traffic jam, and in the end I made it back before DD cracked it. She was generally happy with whatever food and water was there, particularly yoghurt.

I didn't bother expressing, I just used whatever supplies I had (I used to express for comfort when DD dropped a feed for a few days, that kind of thing, so I did have a small stash).

GL! You'll probably find she manages quite fine without you and just has bigger bfs when you get back on the days you work.