If the candidate goes for a second attemt, then no training is required and the candidate, who already has a recomendation for test for that Series, may do as he wishes. The candidate could have even departed the ATO with his certificate so you would have no say in the matter. Any additional training is purely advisary but may be a good idea.
If however the candidate had elected to go directly to Series 2 then the Examiner would mandate a minimum of 2 hours additional training that an ATO must complete before the candidate is issued with a new recommendation for test, for the next Series. A Ghengis says, it would be entirely dependant upon which items had been failed and where the candidate's weaknesses were, as well as any mandatory requirements set by the Examiner. Like the PPL it takes as long as it takes.