I have an upcoming international trip (BER -> EWR -> RTB) on February 4 and need to cancel. The ticket is booked in normal economy (L / W fare classes). When I go to "view cancel options," I am presented with the option to request a future travel credit of 610 EUR.

I would like to do this, but have the following basic questions:

1. What is the deadline for requesting to cancel and receiving a FTC? Ideally I would like to wait as long as possible in case United makes a change to the itinerary and I can get a cash refund.
2. Do I need to use the future travel credit all at once, or can I use it piece-by-piece?
3. UA says change fees may apply when I use the FTC, but none are shown. How do I know what fees, if any, will be charged?

Thank you for your help!