going from dry lot to pasture

I have found a new place to keep Jack and Danee. Jack is currently at the trainer and Danee is still with his momma, so I have some time before they are ready to come to their new home. Sometime around mid September. What is the safest way to transition them to being on grass without foundering. I was thinking of stalling them and letting them out slowly, like an hour, for the first few days and increasing the time every few days. Any ideas?

You are very much on top of how to introduce your horses to being turned out on pasture after being drylotted. Turning one out even in September after most of the greening of spring grass is over there is still a possiblity of grass founder. Your plan is truly a very good one.