Hello Anne,
I fully agree with Elizabeth: I would also say that, having a long period of time before the risk might impact on the project objectives, it should denote a low proximity; i.e., the potential impact is far from you.
Just out of curiosity: the word proximity comes from the Latin word proximus, which means nearest. So you may want to think about it as: the nearest (in time) the impact is, the highest the risk proximity is.
Gabriella