The "2-year" safe harbor is applicable to challenges buy the IRS as to whether a dwelling unit qualifies as property held for productive use in a trade or business or for investment.
See https://www.irs.gov/pub/irs-drop/rp-08-16.pdf
You can generally convert the property to your primary residence safely after that period of time, but you will ultimately be faced with recapture of depreciation and a reduced home sale exclusion as a result of the rental period.
