I volunteered in my kids' classrooms so let me see if I can piece it together.
The most they worked on math in 3rd grade was about 35 minutes five days a week.
Other subjects might have about the same amount of time but there was a lot of project based learning and little direct instruction.
Somewhere in there you must account for all the time it took for classroom management and getting kids settled back in after recesses and lunch.
Art and music were exceptions. Art was closer to 45 to 50 minutes once a week.
Music was 40 minutes twice a week.
We went on a vacation for a week when dd was in 4th grade. When she returned she had completed the entire week's work - including reading in about 2 hours.
