I bought a ticket on a UA flight and there was a schedule change after I did so (which results in a longer layover). The notice I received said that I am entitled to one free change to my flights (or cancellation, if I prefer) as a result of this schedule change.

Is there any time limit for me to use this schedule change? For example, if I received this notice 3 months before my departure date, can I wait to decide what I want and use my "free flight change" a day or two before departure -- subject of course to availability on the flight I want to change to?

And if so, I assume availability would not be required in my fare bucket but instead only in my cabin, correct?