Is it possible to use DateTimePicker (Winforms) to pick both date and time (in the dropdown)? How do you change the custom display of the picked value? Also, is it possible
It is best to use two DateTimePickers for the Job One will be the default for the date section and the second DateTimePicker is for the time portion. Format the second DateTimePicker as follows.
timePortionDateTimePicker.Format = DateTimePickerFormat.Time;
timePortionDateTimePicker.ShowUpDown = true;
The Two should look like this after you capture them

To get the DateTime from both these controls use the following code
DateTime myDate = datePortionDateTimePicker.Value.Date +
timePortionDateTimePicker.Value.TimeOfDay;
To assign the DateTime to both these controls use the following code
datePortionDateTimePicker.Value = myDate.Date;
timePortionDateTimePicker.Value = myDate.TimeOfDay;