According to recent data, about 40% of men have a recurrence at some point after RP but that is partly because men at stage T1, T2 and T3a may all be offered surgery and those with the T2c / T3a are pulling the average down.
My husband had the RP at age 50 with a supposed diagnosed T1a and G7 (3+4) - he had salvage RT 2 years after the op. My dad had undetectable PSA for 18 years post-op and then had a recurrence.
Based on info from many members here over the last 11 years, the 2 year point seems to be significant for recurrence.