Jess2316, your schedule is a lot like mine and I have family watching the kids also. That one day a week at home makes a difference in letting me get quality one-on-one time with the kids and still get some housework done. That leaves our weekends free for family time and date nights. My husband sometimes mentions how much more money I would make if I would work full-time but it's definitely not worth it to me. Even when my youngest starts school, I'd like that extra day to run errands or volunteer in the kids' schools.
Does your mom watch the baby at your house or her house? We have both moms watching the kids and my MIL comes to my house 2 days a week. That saves a lot of time for me in the evening because I don't need to pick up the kids. My mom also sends dinner home with me occasionally which of course is always a big help.
As far as working mom guilt, it will get easier but it does get harder again at 6 months. I think it's partly because the hormones are getting back to normal. The baby also makes a lot of developmental changes at that age, sleeps less during the day, starts to play and coo more and starts to develop a real personality. It's so much more fun playing with the baby than doing housework. I used to do silly dances, sing songs, and play peek-a-boo while working. It took a little longer, but made housework more fun for both of us.