This would depend on how particular your requirements are and whether the start date of the internship period coincides with ongoing university classes!.
From experience we have noticed that interns are easily sourced within a short time period including within 6 days, if the internship start date coincides with a semester break and the intern qualification requirements are not too detailed or specific.
However, generally, please expect the selection process to take around one month. Also we do not guarantee interns for every job position.