The most problematic part of the integration data is insert correct and valid date and time.
tSheet is using Googles datetime object and input validation, but sometimes mistake can be make. Usually the mistake happens when date and time is paste from external source.
In case date and time is not valid or imported date is not correct, follow the next steps.
Set the spreadsheet localization.
In File → Settings Choose your location and confirm selection by Save settings
If the step 1 have not helped, mark cells with the date and set formatting again.
Mark cells with the date time.
Go to Format → Number → Date time
