This is the recommended expression for rounding dates to the beginning of the next plan year quarter:

BOY1_DT:= #NEXTBEGMTH (6 #LSTBUSDAY A_DT) &

; find the last business day of the current plan quarter, then round that last business day
; to the beginning of the next month

A_DT may be either a single date (e.g., 7/16/2015, DOH, #DODEC) or an array of dates (e.g., #DATE).   

We start with #LSTBUSDAY because it's the easiest way to work with plan year quarters, but then we need to use #NEXTBEGMTH to guarantee that we are at the beginning of the next plan year quarter. 6 #LSTBUSDAY A_DT finds the last business day of the current plan year quarter, which is one of the last 3 days of the current plan year quarter, depending on whether the last day of the current plan year quarter is a weekday, Sunday or Saturday. Then #NEXTBEGMTH converts it to the first day of the next month (i.e., the first day of the next plan year quarter).