Hi @mip96 ,
Do you want to limit the end time selection of less than 10 hour from the start time?
If you do, I’m afraid there is no way to achieve your goal currently in PowerApps. But you could create an Hour Validation on your submit button. Below is my demo:

Below is the formula of the Label’s Text, you could set it invisible in your app just for checking the result of If statement, and you could also use two variables to store those two time value so that you would be able to patch them to data source more conveniently.
Set(varST,Text(Concatenate(Text(DatePicker2.SelectedDate)," ",Dropdown1.Selected.Value,":",Dropdown7.Selected.Value),"[$-en-US]mm/dd/yyyy hh:mm:ss"));
Set(varET,Text(Concatenate(Text(DatePicker2_1.SelectedDate)," ",Dropdown1_1.Selected.Value,":",Dropdown7_1.Selected.Value),"[$-en-US]mm/dd/yyyy hh:mm:ss"))
//Create this two variables on a button or apply them on each OnChange of Dropdowns of Date Time picker.
DateDiff(DateTimeValue(varST),DateTimeValue(varET),Minutes) //formula on the Label's Text property
This formula concatenate those two date and time picker results and using DateDiff function with the Minutes parameter to get the difference in minutes of those two time values. After this, you could apply an error message and patch function on the button like below.
If(Value(Label.Text)>600,Set(errorMessage,"Duration could not be more than 10 hours !"),Patch(DataTable,Default(DataTable),{StartTime:varST,EndTime:varET})
Hope this helps.
Best regards,
Community Support Team _ Jeffer Ni
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