I figured out a way to make this work if anyone is concerned. For my first entry:
IF today = dateserial(year(currentdate),month(currentdate),1) to dateserial(year(currentdate),month(currentdate),14) THEN dateserial(year(currentdate),month(currentdate),15) ELSE dateserial(year(currentdate),month(currentdate)+1,1)
second entry:
IF today = dateserial(year(currentdate),month(currentdate),1) to dateserial(year(currentdate),month(currentdate),14) THEN dateserial(year(currentdate),month(currentdate)+1,1) ELSE dateserial(year(currentdate),month(currentdate)+1,15)
etc.