This sets, for incoming R2 registers using non-compelled pulse signaling, how long a received forward digit pulse is allowed to stay on, the timer starts when the pulse begins and runs until the pulse is detected as turned off. This is the receive-side companion to ccasRSTOutFwdPulseOnTimer, so an admin pairing gateways from different vendors needs both ends' pulse-on timing to agree, since this incoming timer is what actually validates whether a received pulse's duration is acceptable. If an incoming pulse is received but held on for longer than this timer allows, the gateway may reject it as an invalid digit rather than a legitimate dialed pulse.