The shift in the construction programme marks the second anniversary of the start of building work.
Specialists will now move in to create the correct ground conditions for the running track and the turf for the field events.
Over the coming months, ducts and a drainage system will be installed and the base layers will be laid in preparation for laying the turf and track next year.
The manufacture of the black and white seats has also started in a factory in Luton and they will start to be fitted into the Stadium later this summer.
John Armitt, ODA Chair said: “Only two years ago, the Stadium site was a flat piece of ground. A huge amount has been achieved since then with the venue now structurally complete and at its full height.
“Work is progressing on covering the roof and the first seats will be fitted this summer. The continuing progress means the Stadium is still on track to be completed a whole year before the 2012 Games.”