The Joint Admission And Matriculation Board has officially confirmed that the 2017 UTME (the actual examination) will commence 6 May and end on 20 May, 2017 (excluding May 12, 2017 because of Candidates sitting for WAEC's Further Mathematics examination).
That simply means that the examination will commence 2 weeks after the end of registration.
You can consult the official JAMB 2017 Registration guidelines for the detailed registration timeline and information.
If there are no challenges, the examination is expected to last for only 14 days.
For candidates who usually wait till after the registration to start preparing for examination, I believe by now you already know it's not going to favour you this time. So you better start reading to avoid touching stories.