If your data includes Dates, Times, DateTimes, or Timestamps, there are some special considerations to keep in mind.
Dates, Times, and DateTimes in spreadsheets
Date, Time, and DateTime formats vary widely across locales. It is important that your worksheet specifies the correct Locale and that all your worksheet data cells are formatted correctly, as described here.
Many spreadsheets use automatic mechanisms to add a Timestamp in the first column. A Timestamp is generally a poor choice for a key -- though it uniquely identifies the row, the Timestamp isn't really meaningful to the rest of the app. So if the Timestamp is chosen as your key, you may need to change that explicitly.
Dates Times, and DateTimes in apps
Dates, Times, and DateTimes are displayed in AppSheet apps based on your mobile device's locale or browser language setting.
If you are seeing the wrong Date, Time, or DateTime format on your mobile device or browser, make sure your mobile device locale and browser language is correct. US English date format is different than non-US English format.
Change your language on Android: https://support.google.com/accounts/answer/32047?source=gsearch&hl=en
Change your language on iPhone / iPad: https://support.apple.com/en-us/HT204031
Change your language on Chrome: https://support.google.com/chrome/answer/173424?hl=en