Exactly, they seem to have been focused on not letting the schedule slip further for quite a long time.The mad thing is that this options appraisal hasn't been done already! Though I'm not sure that tops letting contracts for Euston before determining the construction cost...
HS2/DfT seem to have made an absolute pig's ear of this one.
Now though they appear to have gone the other way in that it is unclear how much how much more "no regrets" at not huge cost stuff they will keep doing on the station and approaches. E.g. Hampstead Bridge western side replacement, the new retaining wall elements, on the western side of the alignment North of Hampstead Road all of which would reduce construction impact locally when complete.