Hi Alexandros,
1) is there a deadline for the completion of the assignment after it's downloaded? ...
Nope.
... can i pay the fee, download the assignment and submit it any time in the future (even in a couple of years)?
That's my understanding. The essay exam voucher however has a one year deadline. I waited to finish the assignment before purchasing the exam voucher.
2) if you have the certification already, how long did it take you to get it?
I started my design in early April and uploaded in late July. So for me roughly 3.5 months. It can certainly be done in a shorter time frame though.
Hope this helps,
Michael Morris
Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction. - Ernst F. Schumacher