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I understand your concern. In grade 1 your son should not be doing more than 10-15 minutes of homework and this should be dedicated to reading, learning words and maybe a bit of counting, maths bonds. The 15 minutes should include his OT exercises. If he has a lot of OT exercises then chat to his therapist to see if she can reduce it, or spend time doing it on the weekend.
As you get home at 5:30 I would suggest you spend the first hour doing something fun with your son so he can attach to you. After bonding with you let him do 5 minutes of OT, then bath and supper. He can do some counting, maths bonds, while helping you set the table and finish supper. After supper at 7:15 do 5 minutes of reading. It is appropriate to do shared reading with him where you do some of the reading and he follows you or you read a sentence and omit one or two words which he reads. Then bed at 7:PM.
Homework is not that important and should never dominate a child's free time or make a child anxious and miserable. Try to make homework as fun as possible and find opportunities such as driving in the car to do some of it. Your son will also benefit by chatting to you on the way to school when you can teach him thinking and problem solving skills.
Spending his time playing, chatting to you or dad, and relaxing is more important for him at this age and if he appears to be burdened with homework, then chat to his teacher and therapist about a plan to reduce it or to offer him additional help.
Please read my articles on my website titled: 'Helping your child study, managing homework stress, homework- 7yr old not coping."