If you're confused already, referencing Section 280A is not exactly a cure . . .

https://www.law.cornell.edu/uscode/text/26/280A

The "conversion" piece is referenced in (d)(4)(A):

"For purposes of applying subsection (c)(5) to deductions allocable to a qualified rental period, a taxpayer shall not be considered to have used a dwelling unit for personal purposes for any day during the taxable year which occurs before or after a qualified rental period described in subparagraph (B)(i)"

So once you "flip the switch" and the unit is available for rent/rented you don't need to apply the vacation home rules to that time period.  In your case, sounds like that's 16 days.  The assumption is that you will meet the qualified rental period of 12 months but we won't know that until December.

Rick