Hi,
Is this a Date value and ACTUAL date value or a string.
If you are putting data in the excel as a DATE value, then its getting converted based on time zone.
Please provide details/explain how you go from the drop downs to a Date / Time in excel.
You are clearing doing something with the drop downs + excel if its turning into a Date Time which you say is not the same between the two. if its just a string then you are doing something wrong. If its a date time, then its an issue being converted from "whatever you have string/date" to a date time in Excel.
Please provide details on how it works from UI to Excel and how it gets there and if the field in Excel is formatted as a date time.