Hello Mauricio,
modern IOS images support sub-second hello timers so you can speed up convergence.
Another possibility if supported is to use BFD (Bidirectional Forwarding detection)
see
OSPF Support for Fast Hello Packets
By specifying the minimal and hello-multiplier keywords with a multiplier argument, you are enabling OSPF fast hello packets. The minimal keyword sets the dead interval to 1 second, and the hello-multiplier value sets the number of hello packets sent during that 1 second, thus providing subsecond or "fast" hello packets.
When fast hello packets are configured on the interface, the hello interval advertised in the hello packets that are sent out this interface is set to 0. The hello interval in the hello packets received over this interface is ignored.
The dead interval must be consistent on a segment, whether it is set to 1 second (for fast hello packets) or set to any other value. The hello multiplier need not be the same for the entire segment as long as at least one hello packet is sent within the dead interval.
http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_osp1.html#wp1014268
then there the SPF timers that can be tuned otherwise the convergence time is 1+5 = 6 seconds.
in router ospf config mode
timers throttle spf
see
http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_osp3.html#wp1017802
Hope to help
Giuseppe
