The build date for me changed 3 times before it finally went live. Just decide what ISP you want to use for fibre and then order ADSL/VDSL from them while you are waiting for fibre. They should allow you to cancel your contract part way through. So you can sign a fibre contract with them.
Thanks for the feedback everyone. Will sit tight and keep an eye on the dates. Probably a good idea above to sign with the 'ultimate' fibre provider so switching will be easier than breaking contract and going elsewhere.