30 seconds is the default “time step” (4.2), but in talking about the transmission delay window (5.2), which the RFC recommends “at most 1 time step”, but also

30 seconds is the default “time step” (4.2), but in talking about the transmission delay window (5.2), which the RFC recommends “at most 1 time step”, but also says that validation should occur for both the previous and next time step window. However in practical implementations, 5 minutes on both sides is typically used.