Array formula (or other) to copy down formula in adjacent cell to last row with data?

Question

I have a spreadsheet in Google Sheets in which the formulas in E2 and F2 need to be copied down to the last row that has data. Here are rows 1 and 2:

Name of Teacher Date Absent During        Start Time          End Time
Larry Smith     2016-04-07  Period 1      4-7-2016 08:40:00   4-7-2016 09:24:00

The formula in E2 is:

=C2+choose(value(regexextract(D2,"\d+")),time(8,40,0),time(9,24,0),time(10,13,0),time(10,57,0),time(11,41,0),time(13,14,0),time(13,58,0),time(14,42,0),time(15,31,0))

The formula in F2 is:

=C2+choose(value(regexextract(D2,"\d+")),time(9,24,0),time(10,8,0),time(10,57,0),time(11,41,0),time(12,25,0),time(13,58,0),time(14,42,0),time(15,31,0),time(16,15,0))

Note: Date of Absence is C2; During is D2.

Is there an arrayformula (other any other) that will see C2:C and D2, then fill the formulas in E2 and F2 down to the last row with a value in C and D?

Here is the link to the spreadsheet.

Answer 1

The way I usually tend to do my arrayformulas, and actually any formula that requires action based on a value in another cell, is i start them off with an ISTEXT statement, and then just a simple comma in place of the else portion:

={"Start Time";arrayformula(IF(ISTEXT(B2:B),text(C2:C+vlookup(D2:D,Administrative!$A$1:$C$10,2,false),"mm-dd-yyyy hh:mm:ss"),))}

Note: the reason I leave just a comma instead of "", is that "" will leave a blank string, which will prevent new entries from being added in those rows if your using google forms or any other integration to add in those entries