How long to get finasteride out of my body?

I took my first 0.25mg of fin yesterday, and today I can’t get an erection. I have no idea if its the compounding fear in the back of my head to check if I have side effects that is preventing my dick to get hard, but I struggle to get “into” porn that would usually get my blood pumping to my member almost immediately. Again, have no idea if its fin or if its in my head, but still I want to wait out the finasteride and see if my dick gets hard again. If it does, then its the fin that caused the ED.

With ED developing in just one day, I suspect you are dealing with a powerful placebo effect, rather than a drug effects; nevertheless, it should be out of your system in less than one month, but I have seen lingering effects last 2-3 months on occasion.  I would stop the finasteride.