24 hours. I usually transfer just over a grand and leave it a bit longer to be safe. I have had issues before where the OD didn't kick in.how long do you have to be in overdraft for R1000
Another way to tell if it worked is to check your detailed balance of your account. If there is an interest accrued charge, it worked.
Doing it over weekends and public holidays is also touch and go for me.
