Simple answer no. If VAT is due it is calcuated at the time of your invoice, irrespective of the terms of payment.
Type vat into the search box ........Wilba .
Not that it would help a great deal but it would have been better to say which cruise line you are booked with. I'm with Richard ( or even Richard Richard) and Wilba in that we don't really know and it has been said several times very recently in answer to very similar questions. Sorry...... Neil.
You are not paying any VAT, so there can be no reduction. Cruises are classed as 'transport' and zero-rated.