There is a finite time to run anything on CS:S, and Valve do not give out any secrets when it comes to coding, especially with the scheduler.
Think on this for a moment. MS Windows has a task scheduler running, all the time in the background, to run various system tasks, some interrupt based, others timer based and of course any network management. Then you start up the Steam portfolio which is now added to the MS task scheduler. You start CS:S up, this is also added to the MS task scheduler. On top of this, you have the game engine task scheduler running which reads sample data back from the server, and sends packets of data back to the server.
Is it any wonder that settings and timings are critical.