I joined on the 737 in Jan 2022 as an experienced FO, final line check was in April, SFO upgrade went through 6 months later in October. The OM-A states 3 "check reports" as a requirement, not specifically sim checks. For me that was the initial LPC/OPC, a line check, and a recurrent sim. No extra stand-in sims or anything like that. You also need the approval of base management who are checking a load of "Personal Performance" and CRM-type requirements too. So it's do-able in that time frame, I'm nobody special. Having said that, not everyone on my intake got the SFO upgrade in minimum time as there's no room for any snags on those 3 checks, those guys will wait until their next check (which will hopefully go smoothly and not delay things too much for them).