This forum (particularly the threads "Your Guide to Spending Avios" and "Chase Miles to Redeem? Start here" have been extraordinarily useful in planning how to redeem my growing stock of Avios--thanks to everyone who contributed to them!

I'm trying to use my 241 voucher to go from JFK-LON in F over the first weekend of May (the 2nd-8th; hoping to tack on an open-jaw LON-GLA/EDI-LON and return LON-PAR-LON within the trip, but those are secondary). At the moment WT and WT+ and some odd J is available, but from recent reading (and looking at availability a few days from now) I know that J and F often open closer to travel dates and that the general advice is to book something now and take the J/F availability when they come up.

Two questions on the mechanics of this:

1) The "Your Guide to Spending Avios" thread indicates that:

"If the booking is cancelled before 24 hours of the first flight, the Avios, taxes, and fees will be refunded, plus the companion voucher. Generally the voucher and Avois will be refunded quite quickly, with the monetary components taking a few more days to process. A cancellation fee will apply unless you are a BAEC Gold card holder."

--How quickly is "quickly"?--I would hate to cancel my WT+ booking and find that the F availability I saw disappeared before my voucher redeposited and I could rebook--if I make the cancellation and rebooking over the phone can it all be done in one fell swoop? I am aware of the nominal cancellation and phone service fees.

--By the same token, my return flight is six days after my departure, and I expect that additional availability may open up in F (I'm a sucker for the CCR) after I've settled on something adequate for the departing flight (and perhaps taken it). On award tickets with the 241 am I stuck to my return details once I take the departing flight?

Thanks to all for your guidance--this forum is superb in providing answers to the seemingly most esoteric and detailed queries!