18.5 doesnt bite, page-17

Striker, with commsec, you buy today, and sell next trading day (monday), then on wed (day 3) they will debit or credit your account the difference. It is T+1 to avoid paying the difference, but T+3 till they debit or credeit there account. It doesn't have to be the same stock that you bought today that you have to sell the next trading day. As long as the amount that you spent on the trade is covered by a sell of any stock on the next trading day, then this rule applies. I have done this and gone weeks without having any debit or credit on my account, due to always covering the cost of the buy with a sell the next trading day