The bank (position x) should provide 100 yabbies in 15 minutes on that tide but don't be too late as it floods very quickly. If you arrive at the sandbank not later than 6.30am you should be okay but only just.
The sand bank is due north of Millionaire's Row, east of Crusoe Island and is the bank just to the north of a small channel leading into the lagoon area on South Stradbroke.
You don't have to get into that small channel and can anchor on the sand bank on the Crusoe Island side of it.
Good luck and hope you have a nice time.