Does how you submit date and time data matter?
The answer is “Yes” if you are using Canvas apps. Depending on if you are submitting your date and time data through the Power Apps UI or using direct oData API call your data will behave differently, but only for User Local data.
The Power Apps Canvas UI performs calculations on submitted date and time data so that it will display properly. When a date and time for a User Local column is added through an app, an offset will be added or subtracted from the data based on the submitting user’s time zone. This is because when the Canvas UI retrieves and displays a User Local field, it will process the current user’s offset of the value. This results in the expected date and time.
Example: The Pacific time zone has a UTC offset of -8. So submitting 4/4/2021 12:00 in the Pacific time zone will add +8 to the time to make sure when it is retrieved the correct original time is displayed. This results in the UTC value 4/4/2021T20:00:00Z.
When you submit directly using the API, the UI is not involved at all. This means submitting4/4/2021 12:00 through the oData API will result in a stored value of 4/4/2021T12:00:00Z. When the API pulls this value for the Pacific time zone user, it will apply the UTC -8 and the displayed result will be 4/4/2021 4:00, Depending on the UTC offset and the time stored, this can result in your data being off by up to an entire day.
This can be easily fixed by applying your own UTC calculation or offset value when submitting via API.
I’ve recently updated this document to outline this information to help ensure your data works as you intend it to.