Well if it was a jet doing 1,000 mph (about twice normal airliners) you can guess about how long would be "gentle" enough. 10 mins or so?
Since we want to stop the earth and there are some big things to slow down and not shake loose then we need to be more gentle. an hour?
It depends on what maximum acceleration you are willing to except (deceleration of course).
Middle east latitue has us at something like say 700 kmh. We want say, 1/10th g
so we want to lose about 1 m/sec/sec.
700 kmh is about 200 m / sec. That means 3 or 4 minutes should do it.
That would generate some damm fine earthquakes here and there I'm sure but it isn't going to kill everyone outright. I think that a lot of ppl would fall over is all.
A couple of hours gives us a 1/100 of a g. I don't know what that feels like but it should leave most temples standing is my guess.
Now we still have to grab hold of it somehow. The mountains are not going to work as handles. Then we need to get rid of the rotational energy. Spreading that over an hour doesn't really help much.
Ya see, it seems it always ends up with a miracle somewhere.