Calculating time using excel formulas

Maybe like this:

      --A-- ---B--- --C-- ---D--- ------------------------------E-------------------------------
  1   Appt  Arrival                                                                             
  2   08:00   10:00 02:00 Late    C2 and down: =ABS(A2-B2)                                      
  3   10:00   09:00 01:00 Early   D2 and down: =CHOOSE(SIGN(A2-B2) + 2, "Late", "On Time", "Early")
  4   10:00   10:00 00:00 On Time