As far as I can tell, there is no expiry time for NQ training. At the time you apply for the qualification, so long as you can produce logbook evidence of having completed the training at some point, it will be valid. But don't take my word for it - ask the CAA for confirmation of this.
If you do plan to delay the application, I would still get the form filled in asap. This is because you will need a signature from your instructor on the form, and if you're going to wait 7 months there's no guarantee the instructor will still be at the same school.
FFF
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