Auto Calculate Shift From Timestamp Field(In Subform)

Auto Calculate Shift From Timestamp Field(In Subform)

Hy ,

I have one sub-form with 2 fields on it.
First field is Timestamp  , which is Date and Time field .  second field is Shift , which is drop-down field with values (a)Early Shift , (b) Late shift.

needed whenever form opens automatically Timestamp field fills up with current  time and date , and  accordingly  if in Timestamp field time is 7-12 then with Early Shift and if Time is 12-6 then with Late Shift .

Please Help me with this . Thank you in Advance .
Hope i get reply soon . Have a nice day ahead :)