Gurucube: There is no "standard overtime" in addition to AAVAs - only AAVAs (part or whole or SOAL).
You cannot do any extra operational hours before or after a shift - that would break scratcoh. You can come in / stay for meetings before / after shifts and be awarded TOIL.
ATCO Additional Voluntary Attendance, Selling of Annual
Leave and Time Off in Lieu Agreement
2.12 Overtime will only be used for extension of shifts or for part-timers (see paragraph 1.3) and not as a substitute for additional attendances.