Great that it was covered by the warranty. I would be interested to understand how the dealer calculated that cost. I would check your engine oil level too as they did not replace mine and it was just above minimum. Did they give you any route cause feedback? Mine was due to a blocked breather pipe.
Just to give you a rough idea on time involved, when the dealer replaced my clutch they said the repair time for a clutch replacement was about 9 hours labour, as it included a 4 wheel alignment due the subframe being removed.
Once you've got the gearbox out and flyweel off, replacing the rear main seal is not a big job.