Indeed as Alex says; DateTimes are always stored UTC. Displaying a value in the timezone is handled by the client, depending on browser timezone and handling on the server based on User timezone, app time zone and server time depending on the configuration.
See this academy module explaining more of this: https://academy.mendix.com/link/module/374/lecture/3046/7.1-Introduction
Additionally, is it required to have the time localized to Singapore time?? If app is only used in Singapore, then don’t localize the value. When user sets time to 9AM, it will be stored as 9AM and displayed and handled on the server as 9AM in all cases
And note; DateTime is always independent from Mendix a pain in the a&$
Do you have localize set to yes?
Mendix will always store dateTime attributes in the DB as UTC and you cannot change that, see: https://docs.mendix.com/refguide/date-and-time-handling