RyanRs, a lot of information has possibly 'sunk in' from the previous study session so having another study session will at times, be a quick revision of what you learnt before. On that basis, in your shoes, I would keep the appointment on the 22nd.
An open question for everyone now; can he book an exam at another school for a date more convenient to him? Would there be acceptance of a certificate from that school by his own?