Why can’t I get the 92Y MOS because classes are 2 months ahead? Does it have to be 90 days or more?

That's HRCs rule. You have to go TDY enroute to your next assignment. It's extremely difficult to do that within 60 days. When you get a class seat that's close, your Career Counselor then has to request a follow on assignment, that's up to 3 weeks. Then your assignment has to go through the validation process. That's one week at the earliest if you have no factors such as MACP or EFMP, in which case 2-4 weeks. Then you have the levy process just to get your orders. There's a few extra weeks to months of wait time if you're going OCONUS and gaining Command Sponsorship and passports for family members. Once you've actually finished levy and received orders then you have to submit for a manual 1610, which can take a while. Plus you have to quarantine two weeks at the school prior to the course starting date. When Soldiers don't meet the time line and miss their class seat, that seat is gone forever. So now that contract has to be renegotiated, adding extra layers of work and heartache.

So, that's why HRC requires 90 days