I only have two and they too stay in the barn at night and on nasty days. As this is my first winter taking care of my own horses, everyday is a learning session. If they stay in all night and all day, it doesn't take long at all, and a little longer if they have been out.
Around 5:30 am I will give the grain and hay if they stay in and change the water so it's not frozen, but if they go out, they just get grain and head straigt for the pasture. Either way still takes about 30 minutes. When I get home around 6:00 pm, I bring them in out of the pasture, do a quick brush job and pick feet, but if they have been in the barn all day, I let them be. My stalls are large enough that after I put fresh hay, water, and more grain in, I can get the dump cart in there too and pick stalls while they eat. My evening chores will last from 30 minutes to an hour depending if they were in or out.
I don't really have a very good workout area yet as our land was just cleared, but I can play in the pasture on the weekends if it's not raining.
Insulated Coveralls are a girls best friend, paired with mud boots, and double socks and gloves, I am usually good to go.
This whole winter thing really does stink!! I was so excited to have my boys home so I can see them everyday, and now it has turned into a chore already since I don't have time to really play with or spend time enjoying them. After the evening is done, I still have cook supper, get a shower, and get to bed before ten. If we bring home takeout or something like that, that gives me an extra hour or so to "just be" with them and sit in their stall and enjoy the smells, sounds, the occasional rub, and tons of kisses.