Much depends on intensity and your level of experience, but a good guideline is that it takes one day for each one hour of an event to fully recover. This means if you ride a six hour century, it would take six days to recover. If you do a 14 hour ironman, give yourself 14 days to fully recover.

However, recovery doesn't mean sitting around on the couch. Typically, you want to do E-A-S-Y rides of no more than 90 minutes (so you don't stress your glycogen stores). Easy rides will actually speed recovery and help prevent deconditioning.