CMB2 toolkit: Compare 2 Dates and validate the Time

Hello i am using the CMB2-toolkit for Wordpress: https://github.com/CMB2/CMB2/wiki/Field-Types

I have a Problem where i have 2 Datetimes, where one is the Starting-Time and the other is the Ending Time. Here is a picture how it looks in the Unserinput and in the Backend:

Now i would like to have an validate, when i have set the Event-End before the Event-Begin then i should be warn me like the attributes or parameter-fields "required=>" or "min=>" (https://github.com/CMB2/CMB2/wiki/Field-Parameters).

I try to fix this but i do not know if i should code this or is it somewhere this solution?

Thank you