Hello Mathias,
The extended deadline (now Sunday 20) is for submissions. It can take some time to get the labs graded after that, but this will be done in parallel with exam grading so that we can report the final marks.
We try to grade the first submissions within a few days form the deadline, whereas second submissions can take a longer time. However, there are situations where the graders are busy with even more urgent things (such as other courses), and then the service can be delayed. I'm very sorry for that. But everyone is guaranteed to get a second chance with all their labs.
With best regards
Aarne.