{"Sunday";"Monday";"Tuesday";"Wednesday";"Thursday";"Friday";"Saturday"}
or Use a separate are for Sunday..Monday..
then try below formula..
[pre]=TEXT(IF(MATCH(DepartDay,WeekName,0)<MATCH(ArriveDay,WeekName,0),
(TODAY()+MATCH(ArriveDay,WeekName,0)+ArriveTime)-
(TODAY()+MATCH(DepartDay,WeekName,0)+DepartTime),
(TODAY()+6+MATCH(DepartDay,WeekName,0)+DepartTime)-
(TODAY()+MATCH(ArriveDay,WeekName,0)+ArriveTime)),
"dd ""Days &"" hh:mm:ss")
=TEXT(
(TODAY()-WEEKDAY(TODAY())+
IF(WEEKDAY(TODAY())>MATCH(ArriveDay,WeekName,0),
MATCH(ArriveDay,WeekName,0)+7,
MATCH(ArriveDay,WeekName,0))
+ArriveTime)
- (TODAY()-WEEKDAY(TODAY())+
IF(WEEKDAY(TODAY())>MATCH(DepartDay,WeekName,0),
MATCH(DepartDay,WeekName,0)+7,
MATCH(DepartDay,WeekName,0))
+DepartTime),
"dd ""Days &"" hh:mm:ss")