If time falls in a certain range

Hello,
I have a sheet that we use 24 hours a day between 2 people on two shifts. At the beginning of our job we enter our initials as such Setup(A1) = Day worker and Setup(A2) = Night worker

During the shift when we enter info into a row..our initials need to be at the end of the row.

What I would like is that if the time is between 6am and 6pm, (time is in Surveys(column D)), I would like the initials of Day Worker to appear in Surveys(column S) and if between 6pm and 6am the initials of Night Worker. And if time column is blank for the column S to be blank of course.

Any suggestions?

This sort of help....however...if lets say D3 is blank then it fills column S with "first initials" How do I make it so it stays blank if there is nothing in D?

That did the trick..Thanks!