OOW, Master, Y4, Y3 & Y2 modules are valid for 3 years from the date of issue of the pass certificate. (The Master Celestial Navigation certificate is valid for 1 year.)
An NoE is valid for 5 years from date of issue, and for 3 years after a successful oral exam.
You must apply for your NoE and book your oral exam with enough time, as once your modules expire, you will have to take them again.
The MCA will only issue a CoC if every certificate is in date.