This differs between lenders and will also usually depend on who the applicant banks with. If the lender uses the same bank as the applicant, they can receive their funds within minutes of being sent. Some lenders are able to do this if a customer banks with any of the Big Four.
With most, customers will need to apply and be approved by a certain time (usually around 2pm) for the funds to be received on the same day. If an applicant needs their loan today, the earlier they apply, the better chance they have.