​@atheer ahmed  You can only do this via workflow as date fields don’t support business rules. Create a state called something like “Preparation - Change”. After creation use this as first sate every change is in. When they’re trying to send this change to the 2nd stage stage (approval) you can do some work with expressions and conditions to check if the date is at least 3 days in the future. Depending on the result you can request the approval or send the change back to preparation and tell the person to use a later start date.

The logic could look like this:

Get the current day

Get the diffinhours from now to the start time

Compare the day to required lead time in hours to the week day (Today: Monday - Earliest possible week day: Thursday. Today: Friday - Earliest possible: Wednesday. As we do not work on the weekend). 

The last step is a bit more difficult in our setup as we have different lead times for every change type.

Hope that helps.