Non Stop Forwarding requires two things: a hardware platform which can continue forwarding while a Route Processor is restarting and ... trust. The neighboring routers have to trust the resetting router to forward traffic despite the fact that the control plane is not available.
NSF timers should reflect the time for an RP switchover whereas routing protocol timers are mainly used for tuning convergence after a network event. As such they serve different purposes and usually IGP timers will be lower than NSF restart timer (120 sec per default).
Have a look at the following two documents, which gave me more understanding of NSF:
"Cisco Nonstop Forwarding with Stateful Switchover Deployment Guide"
Introduction: The "external-out enable" command is available for
configuration under the "router ospf process" in case of the IOS-XR
operating system. This command basically enables advertisement of
intra-area routes on the device as external routes in th...
Introduction Basic configuration for netflow Scale parameters for
netflow Netflow support Architecture Packet flow for netflow Inside the
LC CPU Netflow Cache size, maintenance and memory Sample usage Cache
Size Aging Permanent cache Characteristics Which...