Sint Maarten official website states that the passport needs to be valid for 3 months after planned return trip only for visa required countries. For residents of countries where a visa is not required for entry to Sint Maarten, passport only need to be valid for the duration of stay. A visa is not required for the US, Canada and most European countries. If the entry form is requiring 3 months for all visitors, it seems like the people who designed the program are making their own rules.