S.W.
You plan a daily routine schedule. You break it into am and pm time. Then you break it down into daily chores. Include in this the time for a nap(s) and lunch. After lunch you can prep for dinner, have the nap or go out for a bit.
While your older child is home, you can put a load of laundry in the wash and a load of dishes in the machine to do.
What you need is time management. I know it sounds hard but it is not. You have to make it work for you. I had many things to do and they did not get done until I made up a schedule and stuck to it. After a few weeks I was able to tweak it better. This was done back in the day when there were no disposable diapers and I did them three times a week and made bread two times a week. I made up a menu for the month (as we were paid once a month) and it included a bonus week where I could change up a few meals from the main menu. I purchased what was needed from a list and if it was not on the list it did not get bought.
My son got the school bus around 7:45 am and came home about 3;00 pm. I sometimes had to shovel snow so that I could go out and buy groceries or attend a women's function. Baby stayed in crib until 8:30 am. so shovel snow I would do. Baby gave up morning nap but would take one after lunch (we both did) and then we would continue on our merry way. Dinner was prepped and we would sometimes go out in the snow on the sled for air. When it was warmer we would all go down to the park and dad would pick us up on his way home from work. Oh the snow was like what Boston is getting now except more of it.
You might have to change baby's nap a bit to go to the gym but it could be done.
Good luck to you.
the other S.