How long does it take for EIGRP to declare a route dead and to add a feasible successor to the topology table?
Is there any way to make it faster?
Apparently Mohamed was right and your question is more about how to declare a neighbor dead and not about how to process route replacement.
Yes to declare a neighbor dead more quickly you should decrease the timers.
For EIGRP to declare a neighbor dead depends on the lin.
On high speed link (above 1536Kb) , the Hellos are send every 5 seconds. The Hols timer expires in 15 sec (3*Hello timer).
On low speed link, The hello Timers are send every 6sec , the Hold timer expires in 180sec.
U can manually modify the (Hello & Hold) timers, but be sure the Hold timer should be 3*hello timer. You may also find another consideration/precaution about changing it that I may not be aware of but its possible.