Exercise 3: Registering on 20 September — In Time or Not? — Possible Solution
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This person registered in time. This chapter's own real deadline for
registering with HMRC, for someone who needs to file for the first
time or didn't file the previous year, is 5 October following the end
of the relevant tax year. Registering on 20 September is genuinely
before that 5 October cutoff, so this registration meets the real
deadline with about two weeks to spare.

The next real deadline that applies to them depends on how they choose
to file: 31 October if filing a paper return, or the later 31 January
deadline if filing online - and 31 January is also the real deadline
for actually paying any tax owed, regardless of which format the
return itself was filed in. If HMRC ends up requiring payments on
account for the following year, a further 31 July deadline would also
apply to them, but that's a separate, later obligation from this
year's own filing and payment.

ANSWER: Yes, registering on 20 September is in time, since it's before
the real 5 October deadline. The next real deadline is either 31
October (paper return) or 31 January (online return), with 31 January
also being the real deadline to pay any tax owed - regardless of which
filing method is used, the tax itself must be paid by 31 January.

WHY THIS WORKS AS AN ANSWER
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This correctly checks the given date against the real 5 October
registration deadline and identifies the next real deadlines that
follow, distinguishing the filing deadline (which varies by method)
from the payment deadline (which doesn't).