Also talk to your daycare- they will take your son in if you need medical treatment. They always keep 1-2 spots free or will go over their numbers in an emergency.
Use a babysitter if that's cheaper than daycare. Or as @Albert01 said, you need to decide what's more important. A 5-6pm appt with a psych is better for you long term than not going cos your ds needs his wind down. YOU are important. YOUR needs are important. YOUR health is paramount. Tell your dh to get home earlier on a certain day and put yourself first.