The only real way to look at times for an RMA would be to consider:
* who you are dealing with - they may have a policy defining time frames
* how long shipping to and from you will be - they may process an RMA in a day but it takes 4 weeks in the mail....who knows, check the distances!
* does the policy define sending your product to manufacturer or not? that would mean more time as well
Look into those points and you will be able to get a realistic for you and your situation time frame estimate.