When you initiate a transfer out of a clearing bank (like BoI), the money will leave that bank that (working) day, or possible the next (working) day, depending on the cut-off.
After that, they no longer have the funds. RABO are not a clearing bank so there may be additional delays in them receiving the money.
If you initiated the transfer on 13 Sep (Sat), then it would be Monday evening before that money left BoI, so today would be the earliest that RABO could receive it.