Mendix always saves a datetime attribute as a date and time value. If you only need a date, it still saves it in the database as a 00:00 time. Vice versa it also needs a date, if you only need the time.
If you only need the time then you can render that on the page typically as a time. If you upload a time value, I suggest to parse the date in the excel importer flow. You can upload the values as strings and then use the parseDateTime(UTC)() functions to create a datetime value you need out of it. You can do this parsing in the import flow already if you need to.
Furthermore especially with times please be aware of timezones if relevant that can also give you different times then you would like to display.