What is the DTMF duration range acceptable by the CF220?

3.2.5.4.3 Dual-Tone Multifrequency Signaling

3.2.5.4.3.5 Timing Requirements

The tone-on pulse length is at least 50 ms, and the tone-off interval is at least 45 ms. The period (cycle time) is at least 100 ms measured from tone-on to tone-on, or from tone-off to tone-off. By definition, the tone-on interval starts when both frequencies have achieved levels within 1 dB of their ultimate steady-state values. The tone-on interval ends when either component has dropped more than 1 dB below the steady state tone-on level, except for transients described in "Transients", Section 3.2.5.4.3.8 . The tone-off interval is that time interval during which at least one frequency is at a level below -55 dBm0.