Hi @DustyJordan ,
Try reviewing your DB feature class settings. If you have access to it via an ArcGIS Enterprise then you should review how your feature class is set up. If you are using AGOL, then it most likely set in UTC+0. Else, review how service JSON parameters.
Excel is notorious for mishandling datetimes (and data in general). When you write to your feature service, it will write it to an epoch timestamp relative to the feature class' time setting. It is best to open your export in a text format like csv and open it in a text editor.
Users uploading 12-14 hours prior to the service time may be correct as the data is stored in UTC+0 but your application is viewing it as UTC+xHours.
Unfortunately, it is difficult to hit a default setting on a data source/service without having to alter/rebuild/migrate existing data structures. The field usually does not contain the time setting. It is at the data source. Your applications should handle the time difference as describe by your service (which is usually derived from the data source).
Have you enabled change tracking on your feature service? This may reveal how your times are written in your database.