Well the rule is that you have to be their customer for at least 3 months. The rest is hazy and even the reps do not know off hand.
They can put up a request anytime, but it might or might not get approved.
It all depends upon the rep putting it in and the rep who is approving it. Whether they had a good day or a bad day, good mood or a bad mood, what quality score they got when they were last monitored, whether it is a weekend, or maybe the guys average call time is more than the 10 minutes auth by tmobile/client logic and he/she just wants you off the phone, or maybe the agent is dying to go to the washroom (they are not allowed to go outside their brakes) and puts you on a 2 min hold presumably to check out things for you and goes to the washroom, then comes back and tells you no way and adds "Is their anything else I can do for you".
The best thing to do is to thank the rep, hang up and call again and chances are that you will find a rep who will just do it for you. Always be nice and you will get your way. The rules are there but they are all flexable. You might be surprised to know that the supervisor can actully give you a credit of $ 200 if you present your case properly and are consistent. On the other hand if you are nasty because you have been holding for 20 minutes you might get the standard $ 5 for the inconvinence caused.
Also call on weekend morning to get to the rep in the shortest possible time.
Hope this helps
Regards