If you hold The Platinum Card from American Express, you will probably want to use that card when you stay at a participating Hilton property since it gives you S$200 back for spending S$500 (up to 3 times per card) if you have saved the offer back then. For properties that do not participate in that amazing offer, you may be able to earn double points at all participating hotels in Asia-Pacific when you stay between 01 July 2019 and 30 September 2019 and pay for your stay using an eligible Visa card.
There is a long list of participating hotels in this promotion and remember that this will most likely stack with whatever that is happening in the market. At the time of writing, you will already be able to earn double points (06 May 2019 to 09 September 2019)across all participating properties worldwide if you have signed-up for the offer. If you are staying in an eligible property in Asia-Pacific from 01 July 2019 to 09 September 2019, there is a great chance (almost 100%) that these promotions will stack - this means that you can easily earn 40 Hilton Honors Points per USD as a Diamond Member (and pick up your milestone bonuses along the way).
The maximum number of Hilton Honors points that a member can earn from this offer is capped at 20,000 bonus points (essentially USD 2,000 spend) and the terms do state that the stays have to be booked and consumed during the promotional period in order for it to be valid. I have until the end of 30 September 2019 to make use of my ridiculously-impressive American Express offer but I will certainly pay using one of my Visa cards when staying at a property or country that is not covered by that aforementioned offer to pick up some additional points along the way.
[ H/T: John from LoyaltyLobby)