How to validate the wrong date time entry in SharePoint using column validation?

Question

I got these 3 fields in the form where in text form my colleges input date and time. But sometimes they put in wrong times in the fields, and I want a validation for that.

See the picture, if "Ärende påbörjat" is less than "Ärende tilldelad" and "Ärende tilldelad" is less than "Ärende inkommet" I want it to give a warning.

I also want it to be possible to leave the fields empty and save the form. I've tried myself but cant solve it.

Answer 1

Navigate to List Settings->Validation settings->add the following formula:

=AND([Ärende inkommet]<[Ärende tilldelad],[Ärende tilldelad]<[Ärende påbörjat])