There is no constraint as such. As the initial approval period is changed to 2 years all you need to show is 12 months salary evidence prior to appy for extension. So theoritically you can hold up your travel to UK for an year after you get your EC.
But you would have given 6 months time to apply for EC from the date you got your approval. So I suggest in case you cannot apply immediately you still have time till oct 07. Apply close to your departure date.
if your notice period with current employer is 1 month then get EC, resign and travel to UK in months time. In this case you potentially waste a month of stamped visa period.
But keep in mind UK market is very good in between Apr - Oct. Close to cristmas market will be a bit low.
best wishes,
Azlan
(For career advise and billing services in UK contact
Azlan.san@gmail.com)