If I were doing calculations, I'd add a few buffers. Two years to get from 0 to ATP is a very difficult situation. I'd say a fair expectation is to be instructing between 2 and 3 years. You should also plan to be at a regional for no less than 4-6 years (2-3 years to upgrade at the shortest and 2-3 years to get 1000 TPIC). Again, these are the absolute shortest times I'd be using when making a decision. Make sure you are okay with making between 18-30k for 4 years.