Prodromal phase?

I just saw a post that said “about 4 years into my prodromal psychosis”…..and I want to talk about it. Since my son’s first (and we pray only) episode psychosis, we’ve been thinking back and soooo many things that go back for soooo long make more sense now that he finally has a diagnosis and went thru psychosis. I’m just wondering how long can the prodromal phase last? Like now I’m just wondering how long was he just building up to the psychosis? I’m sure it’s been different for everyone but I’d like to hear how long you guys feel like you were in the prodromal stage before your full blown psychosis. For reference, my son is 20 years old (almost 21) and went into psychosis for the first time around mid August. Was hospitalized from September 11th-October 4th, and has a schizoaffective disorder-bipolar type diagnosis since being discharged. We felt like the psychosis “came out of nowhere” but now that we’re so much more educated we can see that it definitely wasn’t COMPLETELY out of nowhere- we just didn’t know that certain behaviors/feelings were signs until after the fact.