In my post on Optimizing my POSB Invest-Saver Plan, I shared that changes to the monthly investment amount only takes effect on the next next month. This information was provided to me by the POSB staff.
However, a few days later.......
The following screenshot from my iBanking account shows otherwise.
There's another point to be noted though. On the night itself (9 March 2017) when I made the change in contribution amount from $200/month to $100/month, the monthly contribution amount is still reflected in the system as $200/month. I did not pay attention to when exactly was my change request updated in the system. Who knows? It could have been the next working day (10 March 2017).
Whatever the case, when I do tweak my monthly contribution amount in the future, I'm going to set one buffer day for the changes to be reflected in the system.