I've seen some of the the 10% posts and that sounds good, for me that makes 5 steps (if I have it figured out right).
0= 252
1= 227 & The first step gets me past my unpassable 230 mark!
2= 204
3= 184
4= 166
5= 149

Any idea how long I might want to give each 10%, 2 months? more? should it change as I drop?

I'm of the opinion that you just give it as long as it takes. Setting time goals can be really tricky. Time goals works for some and not for others, and the disappointment of not making a goal can throw a person off track. A reasonable weight loss is 1-2 lbs a week so if you really want to make a time goal, use that as your guide. The closer you get to goal, often the longer it takes so be sure to adjust for that.