Hi @cekberg ,
Could you tell me how do you update this field by using datepicker?
Actually, the datepicker will not record time value, it only record date value.
For example, if you use Datepicker1.SelectedDate, it will not represent the date that you selected.
So If you use this to update, the time value is empty, then it will be filled will the default value "12AM".
I suggest you use a datepicker to record date and two drop downs to record time.
I've made a similar test for your reference:
1)set the date picker's DefaultDate: Today()
set the drop down1's Default:Hour(Now())
set the drop down2's Default:Minute(Now())

2)if the date type is datetime, use this formula to update:
Patch(listname,Defaults(listname){fiedname: detepicker1.SelectedDate+Time(dropdown1.Selected.Value,dropdown2.Selected.Value,0)})
if the data type is text, use this formula to update:
Text(DatePicker1.SelectedDate+Time(Dropdown1.Selected.Value,Dropdown2.Selected.Value,0),DateTimeFormat.ShortDateTime)
Best regards,