How many years are needed in public to not be excluded from future controller/cfo positions?

Currently an intern at a mid tier firm trying to plan out my career. Obviously I cannot handle the slop that is being fed down my throat in public forever so I'm planning my exit before I have even really started. I don't care about going to B4 because I'm not a cool kid and smaller public firms are more my forte, so I'm fine with missing out on F500 exit ops. However, what is the minimum public experience in general that you all further along in your careers have seen needed for controller and cfo positions in smaller/midsized industry companies? I think the most I can do in public is 3 years because I don't like the culture and am a back office kinda guy. I know this isn't enough to jump into a controller job, but my future self wants to know if I am screwing up by wanting to dip this early? If that's the case I'm fine being a life long senior accountant somewhere in industry.

Tldr: intern wondering about minimum public experience needed to not be excluded for controller and cfo positions in smaller/midsized industry companies.