Data Validation List Selection

Do you want this to happen for all of them?

DD1=7:00
DD2=7:15
DD3=7:30

Or, how do you want the other DD's handled?

In essence, the DD formula would look something like this...
=OFFSET($M$5,MATCH($G$4,$M$5:$M$23,0),0,30,1)

I used a small range, so adjust as needed

In other words, you want to remove from the selection list any items that have already been selected?

It's for a work-day time sheet. Workers are required to keep a log of start and finish times for each task they complete through the day. The start-time column (E4:E18) automatically populates based on the last finish-time entry one row above in the G column (E5 is a copy of G4). The user only needs to enter up to 15 finish-times with the drop-down menu's in G4:G18. After the worker enters a finish-time he no longer needs to see older time selections. I wanted to eliminate all the earlier times from the next menu selection list. i.e. a typical entry: E4 is hard-set at 12:00AM. The workers fist selection in G4 might be 7:00AM and over in I4 he selects "Off-Duty". E5 would then automatically be 7:00AM and using menu G5 he might select 8:00AM and in I5 enter "Driving". E6 would then be 8:00AM and he perhaps selects 11:30AM in G6 and "Working without driving" in I6, and so on. I want only the remaining unused times to appear in as-yet unused menu's to make it quicker to find the needed time entry (there are a total of 97) and I want the menu's to open at the top of the list displayed not the bottom.

For better understanding please attach sample excel file, remove sensitive data if any your file

used named range for data validation