I've been having interesting conversations with talktalk business fttp provisioning as a talktalk business partner, they don't allow you to order until their backhaul is in place. Which can take a minimum of six weeks after it goes live with BT wholesale.
I notice something similar with residential service on new FTTP rollout. I checked daily after seeing the CBT on the pole that my line is connected to. As soon as BTW checker said FTTP was available at 1000Mbps, I could have ordered a 900 service with BT & Zen, but neither TT or Sky were not offering FTTP straight away. A while later my neighbour was able to upgrade his Sky connection, but the maximum Sky could offer him was 500. I think I checked TT at the time, and it was similar, neither Sky or TT were offering 900. I just checked now Sky are offering 900 service on the postcode. This does suggest there is a lag with Sky/TT vs BTW.