When the system seizes a line to place a Speed Dial call, it waits this interval for dial tone before outdialing the call. The system requires that the first dial tone be at least 5 seconds long and the second dial tone to be at least 2.5 seconds long.
Be sure the value you enter is compatible with the local telco. If you set this value too short, the system may not seize properly functioning lines. If too long, there will be too long a delay before the system skips over a defective line.