Hi,
Did you check on documentation, if the format mmm is implemented in this mask?
other situation, can be about the format time of your server:
The OutSystems platform has a default DataTime format which can be set in ServiceCenter. This is the format OutSystems expects when entering a date time in an input. When your mask is requiring a different format, you have to have a variable with type Text in order to get the correct value. In the action that uses the date time, you have to change the Text variable into a Date Time variable in order for OutSystem to understand the Date Time value. In the preparation of your screen you have to have an action that converts the Date Time into the Text including the correct formatting for the custom mask to understand.
Cheers,
Nuno Verdasca