> people tend to lose money on housing in NYC unless it's held for many years.

I'd generally consider that a success metric? People making money flipping houses on short terms is a bad thing

What's a reasonable time horizon?

What should happen when you find a mate and need more space than you did when you moved into your current unit?

A friend moved out of his space after 7 years to start a family, and the appreciation didn't cover the closing costs.