You only need one year as a platinum member. It is mathematically impossible to qualify for lifetime status after twelve years without averaging more than 75 nights/year for twelve consecutive years. Of course, you could do this by spending 800 paid nights in 4 years and doing the additional 200 nights over the following 8 years. This is just one possible example where you might be silver for most of the time and still be able to get lifetime platinum, assuming you also earned 3 million points in that time period.