Time between 2 dates and times

Hi, I have a col with pick dates (K) and a col with pick times(J) I want to find the how much time it took the picker to pick all the orders in a week.

Trying this:Getting a type mismatch error

StartDay = Cells(22, "K") 'small date
  stime = Cells(22, "J")    'start time
EndDay = Cells(lrow, "K") 'large date
  etime = Cells(lrow, "J") ' end time
 
Results = DateDiff("h", StartDay & " " & stime, EndDay & " " & etime)

Can someone advise, thank you Mike