After patiently waited for a month, I finally emailed oracle last week about my assignment. Yesterday, I heard them back and apprently they didn't receive my assignment
I guess i really should not rely on their auto-reply confirmation and should have email them earlier.
Indeed, grading takes between 4 to 6 weeks. But nowadays mostly results are given after 4 weeks (and a few days).
What I did after submitting and taking my essay exam, was sending a mail to ask if they received everything and were able to grade my assignment (I submitted when Sun was still Sun and we had to use a website to upload our assignment, so there was no auto-reply confirmation at all)