The DateTime field must be set to "Edit date/time" before it can be sent to Excel.
If "Edit date/time" is selected, you will be able to see an "Update" field. This is the data that will be sent to Excel.
If you select "View text" there will not be an "Update" field which means no data will be sent to Excel.
If you want to display a date/time, but do not want it to be editable, you can add 2 feilds, One "Edit date/time" and the other "Veiw text." You can then set "Visible" = false on the "Edit date/time" field.