The First Module

was a heavy one, the weight was more than 8,000 tons. It was lifted from the barge in the middle of the night. After midnight the module was lowered on the Spar buoy. It is clearly to be seen that the buoy is considerably lower in the water.

A picture of the lifting during dark hours is on this site

Now the Thialf is on DP within crane and gangway reach of the platform (it isn't a buoy anymore in my point of view)
Welders are busy to weld the module to the buoy, making the platform ready to receive the next module.