Throughout the tillering process, even from the beginning before it starts, I strive to keep the limbs even. If I have a stave with one reflexed limb and the other deflexed, I will definitely heat correct one (or both) of the limbs before I begin. I'm working on an ash ELB stave at the moment, with one reflexed limb (about 1.5") and the other limb is deflexed with a bump mid-limb. Before I even floor tiller, I'm going to heat correct BOTH limbs, making them more even.
Also, the speed at which you tiller has no effect. As long as your tiller remains even and appropriate, it doesn't matter squat how fast or slow you go. And I've never noticed the tiller changes on any of my bows, after a week, a month, or a year. If a bow is stressed and tillered evenly, it will likely stay that way.