Only 9 stations because
Let's say monitoring station release the token at time x, then
1. token will travel the whole ring, time to propagate=10 microseconds
2. token will travel the other 9 stations, which will hold the token for 2 microsec each (18 microsec in all)
3. after that it will reach the monitoring token again. At this point of time it will be expecting the token to come back. that means it is expecting the token to be back at x+28microsecs.
So it will have to wait 28 microsecs before it can infer token is lost.