I've seen both 4 hours and 2 hours. 4 hours is usually acceptable, just make sure that none of your customers require it to be completed sooner than that (if one of them requires a 2 hour window then you must be able to demonstrate you can meet that timeline).
Obviously the return of product is not going to be completed in that time frame, but you need to be able to identify what customers received affected material within the designated time frame.
We're a paper converter making flexible food packaging. We conduct a traceability exercise twice per year and a full mock recall once per year. For the full mock recall I assembled the recall team together and went through a recall scenario raw material forward (we just received word from our supplier that a specific grade of paper was affected). I kept minutes of the exercise (noting start time and end time) including a draft of the press release, draft email notifying affected customers. While we were working on the press release and email details we had the responsible person carrying out the traceability exercise. We also had to identify and isolate potentially affected product in our warehouse as per our Material Hold procedure. We were able to complete the full exercise within the designated time frame. After the exercise the recall team signed the minutes and I filed the signed minutes along with the drafts noted above. This was acceptable with our SQF auditor.
Hope this helps!