Use the system clock to check when the last query has been sent, and don't send another until a certain time has elapsed. You can change seekbar's value as you want, but the query will be sent only every X milliseconds.
static long sendInterval = 600; //milliseconds
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
long nextSend = 0;
}
@Override
public void onProgressChanged(......) {
if (nextSend < uptimeMillis()) {
...send the query and parse feedback...
nextSend = uptimeMillis() + sendInterval ;
}
Start with nextSend = 0, so the first time the query will be sent immediatly. Choose sendInterval value according to server's response time. Start with a high value and decrease until you see that all is working well. If the query itself and the response are small (a few bytes) consider using UDP instead of TCP, it's faster and you can use lower values of sendInterval.