debug onair: add get_duration to nonstop slot

panikdb/emissions/models.py

@@ -280,5 +280,8 @@ class Nonstop(models.Model):
     start = models.TimeField()
     end = models.TimeField()
 
+    def get_duration(self):
+            return self.start - self.end
+
     def __unicode__(self):
         return self.title