You need to read all the stuff on the KCC secondary schools admissions page including the information booklet which is available on pdf on there and make sure you have read TGSWB own admission policy which will tell you which addresses / parishes etc get priority if the school is oversubscribed.
Here is a paragraph I have lifted for you:
Kent County Council will also be able to amend applications
if asked to do so no later than 8 December 2017 with regard
to house moves or changes of schools relating to house
moves provided you have an exchange of contracts or a
signed rental agreement for the new property. It may not be
possible to submit these changes online. Parents should email
kentonlineadmissions@kent.gov.uk with the details of their
required amendment, ensuring that they contact us with the
same email address used for their application.
Yes, it is possible that TWGSB could be oversubscribed with people wanting places and what your address is on 8 December 2017 could affect whether not you are given a place there on 1 March 2018.