ordaz13:
I know that the sum of the delays and the running time must be equal to the desired time, but due to the speed of the servo it finishes before the time.
If you use millis() to manage your timing it will automatically take account of the time in other activities. Have a look at how it is done in the demo Several Things at a Time.
The demo also includes code to move a servo in small increments.
You have not told us how precise your timing needs to be? is an error of 100 millisecs OK?
...R