Normally expire date of voucher is 1 year (except voucher for an assignment that have no expire date) and you must take an exam before expire date. If you purchase voucher on June 2007 the expire day may be 30 June 2008 (which is passed ) or you may lucky get the voucher that expire on 31 July 2008. I suggest you should contact sun's training center to let them check expire date for you as fast as possible.
Wish you lucky. [ July 01, 2008: Message edited by: Soroj Margun ]
I have bought only the assignment. I did not get the essay voucher yet. Assignment validity, I read, is before 18 months after the next major release, which is Java 6. Is it 18 months since Java 6 is released? If yes can I still take the Java 5 exam?
18 months period is a constraint for JDK that you should use. Sun is try force you to use the newest release of JDK. You can look at this release information for release date. I suggest you to read best faqs about SCJD at JavaRanch SCJD faqs for more information.