We have to consider the impact this could have on the sectors further down route. The traffic managers use a system called TLPD (Traffic Loading Prediction Device) which, as it sounds, predicts traffic loading in sectors at a certain time and is based on EOBTs. It is only as accurate as the information put into it.
The impact of inaccurate data in TLPD will be felt the closer you get to the initial entry sector rather than further down route. TLPD will have the flight showing in green (planned but not active), possibly dark green (planned, not active, and past the EOBT), and then change to red when active. However, updated times will then be calculated based on live data (radar and other) and so the further away the sector is, there will be more notice of changes in traffic levels and the ability to take appropriate action, hopefully resulting in the impact being managed.