You get switched to long term capital gains 1 year after exercise or two years after the grant start date, whichever is later.
Not sure what the best source on this is, but a quick DDGing:
https://www.fool.com/knowledge-center/tax-rate-on-exercising...
If I early exercise my options on day 1, then I still have to wait until the 2 years after the grant date (2 years of employment) to get long term capital gains treatment.
If I wait 4 years, then exercise, then I have already satisfied the 2 years post-grant requirement, but I still have to wait a year after the exercise to get long term capital gains treatment.
The key part was my last clause: "whichever is later".