If you become silver in Sept then your year will be roughly the same as your partner's. However if you are aiming to become Gold this may be more tricky, as your last qualifying flight will have to be next year september (but before the day that you became silver).
In that case that also means you'll have to wait the whole year to become Gold and enjoy the benefits. While if you would try to qualify as quickly as possible, you may gain the Gold status earlier. Its just that then you won't be 'in sync'..