KARFA

I assume this is just a flights only booking and not a BA holidays one (i,e. combined flights & hotel/car)?

You can request future travel vouchers as late as an hour before check in closes. I agree it's unlikely your flights will be cancelled now, but there is no harm in waiting say to the day before and then request the future travel voucher. The vouchers are being issued pretty quickly now, so one you apply expect to get the email within an hour or two.

Loads more information and advice threads on the BA board.