in my experience, a D-rest of 3 to 5 degrees with about 25% to go is my goal. However, I have had many instances where I had to choose to bump up the temp early, or not at all due to having to travel out of town. I have found that anywhere after 50% done seems to give the same results.
The only other bit of advice I would give is even when you have a steady final gravity, you may need to leave the beer alone for another week or two. Taste the beer when you think it is done, and look at it too. I find that at 8 to 11 days, the beer is at a steady gravity, but still cloudy and depending on the yeast, I still detect diacetyl. The cloudy is yeast still in suspension doing what they need to do for the lager.... dont cold crash yet if the yeast is still clouding the beer... let them do their work. Let the beer stay at the d-rest temp for up to another two to three weeks. (I have not had good results with the cool one or two degrees a day many people do).
I find that the yeast will settle out just fine given time, and time is what the yeast need to clean ther beer up.