Wait until they send you a promotional e-mail. It will show how many points you have and the actual expiration date. I don't see the expiration date on the web site.

At the top of any promotional e-mail that I receive, I see -

My Name
xxxxxx Rewards points (1)
Until: 09/08/2018

Card Platinum :
xxxxxxxxxxxxxxxxxx
Until: 31/12/2017

Based on what I have seen, if you earn a point, it extends your validity for one year from the date that the point is credited.