Hi Scott,
Okay, I got that clarified. 
Option 1 –  10% is paid in the first 3 days – 5% as a preliminary deposit and a further 5% when the Sale and Purchase Agreement is signed.  (let's say 15 March).  Then another 5% 3 months later (15 June) , and again 5% on 15 Sept.  Total 20%.  Then six months later on 15 March 2009, we pay the remaining 80%.
Option 2 – Sorry, the discount is 4% not 5%.  5% of $5.4M down when the preliminary contract is signed.    And the remaining 95% to be paid within 30 days (so one month to arrange mortgage finance).   The completion date of the property is 31 May.  If the property is not ready for habitation on that date, then the developer pays the mortgage on a daily basis until the property is ready.  So with this option we earn interest on all our GBP and NZD, except 5%, for only 30 days.
So what's the most economical option?
FYI, the developer is holding off selling at the moment because they know the US will drop its interest rate again next week.  The $HK is pegged to the $US so will have to follow suit.  We predict that on 20 March the interest on mortgages will drop to 2.6%, even though inflation is 3.8%.  And our agent has just advised that the apartment we have bid $5.4M for may be offered to us at $5,550,000.  We're living in very hot times over here!