No one can tell you, exactly, when you'll move up. Besides, WGT has never divulged that criteria. I can tell you, from experience, the criteria was mostly based on scoring average...at least before "The Change".
But be careful, one of the first things players learn around here, is they can lower their scoring average quickly by only posting their best rounds. The next thing they learn, the hard way, is there is no going back after realizing they are not competitive in the new tier (The forums are full of stories like that). No, I'm not suggesting sandbagging...but you can avoid this trap by posting all your scores and play your best, then you should stay in the tier where you belong.
Joey