Do I have 11 months to use it then it stops working or do I have 2 months from the point of activation?

I’m looking at getting a continuous pass but it say you have up to 11 months to active and use it. I’m looking to start travelling in April for 2 months but I’m not sure if it would still be valid in May/June as I would still be travelling but it would have then passed the 11 months. Do I have 11 months to use it then it stops working or do I have 2 months from the point of activation. Sorry if this is confusing would appreciate some help.