would it be better to get high off of THC and CBD before or after taking your ssri

Define better?

I am not a doctor and you should really talk to yours.

SSRIs stay in your system forever and take a while to build up. Timing a fast drug like THC with that doesn't matter imo, though I bet there is some acutely larger amount in the blood after taking it.
That being said I take my ssri in the morning and take an edible at night if I am going to.