Hi @Anonymous ,
Do you want to automatically fill in datetime datacard by using date and time in other fields?
I've made a similar test for your reference:
1)control for date field named DataCardValue19
control for time field named Dropdown1, Dropdown2
control for datetime field named DateValue1, HourValue1, MinuteValue1
2)for date datacard
set DataCardValue19's OnChange:
Set(var1,true)
3)for time datacard
set Dropdown1's Items:
["00","01","02","03","04","05","06","07","08","09","10","11","12","13","14","15","16","17","18","19","20","21","22","23"]
set Dropdown1's OnChange:
Set(var2,true)
set Dropdown2's Items:
["00","01","02","03","04","05","06","07","08","09","10","11","12","13","14","15","16","17","18","19","20","21","22","23","24","25","26","27","28","29","30","31","32","33","34","35","36","37","38","39","40","41","42","43","44","45","46","47","48","49","50","51","52","53","54","55","56","57","58","59"]
set Dropdown2's OnChange:
Set(var3,true)
set time datacard's Update:
Dropdown1.Selected.Value&":"&Dropdown2.Selected.Value
//I set time field as text type
4)for datetime datacard(I set this field as datetime data type)
DateValue1's DefaultDate:
If(var1,DataCardValue19.SelectedDate,Parent.Default)
HourValue1's Default:
If(var2,Dropdown1.Selected.Value,Text(Hour(Parent.Default),"[$-en-US]00"))
MinuteValue1's Default:
If(var3,Dropdown2.Selected.Value,Text(Minute(Parent.Default),"[$-en-US]00"))
//Then at the beginning controls in this datacard display as this item's data. If you make any change in date field or time field, data will be automatically filled inn datetime field.

Best regards,