Sure. Somebody could get hired on with a regional after 90 days of flight training. Provided that they trained every day for at least 2.75 hours of flying and did absolutely perfect on every lesson and didn't have any weather delays or issues scheduling aircraft/checkrides, etc.

But you show me one person that's made it zero time to hired with a US 121 regional in 90 days, and I'll buy you dinner at a nice steakhouse of your choosing.