It sounds like you are using time to determine when to take them up to rest. I use the bend test, others the toothpick test. Here is my method.
For spare ribs, I wait until there is little less than 1/2 inch of pullback from the end of the bones before doing the bend test. There is only about a 15-20 minute window between sagging and actually giving it up and going limp. I thinly glaze them the last 15 minutes
I then take them up, wrap in butcher paper and hold at 170 degrees, usually in my oven, for at least an hour, but it can be for a couple of hours. (Thanks to Brother Gig'em99 for the inspiration for this holding technique.)
These were fairly thin and cooked hot and fast in just over two hours before passing the bend test, wrapping and popping in the 170 degree oven.