what is the usual validity for RTR (C)
Validity will be on your NTC validity date, ie till your NTC is valid you will get RTR(C).
Suppose your NTC is valid till 2014 July then you will get RTR(C) till July 2014 Or if validity is till July 2012 then RTR(C) will be valid till July 2012.
You will get RTR(C) only if you clear Part 1 and have 30 hours in 36 months from your renewal date.