I have Wrapper class which contains List of Map. After performing some operations that List values order gets changed.

public Class TeacherWrapper{
     public Map<Date,List<Session__c>> dateSession{set;get;}
     public TeacherAvailabilityWrapper(){
           dateSession= new Map<Date,List<Session__c>>();
     }
}

Now I want to sort List<Session__c> of dateSession. Based on Start_time__c (DateTime)field in session.

How to achieve it using Comparable interface?