The standard North American ring pattern is 2 sec on, 4 sec off, repeating, so:
60;(2+4)
which will ring that pattern for 60 seconds. (It's the Bellcore-dr1 ring, Ring Pattern 1 in Ring Profile A. It should be there, just choose Profile A in the service (Voice Services/Service SP1, or SP2 or whichever you want it for), and choose 1 for X_DefaultRing (either by connecting directly to the 202 or, preferably, by using Expert Mode in the dashboard).