to simplify this go to routergods.com there a video tutorial on how to set up ntp master and ntp client,
but read the doc. as well in order to understand the theory behind it.
Getting the NTP setup and running would be a great thing and good added knowledge.
I am pretty positive that I have tested running these EIGRP Auth labs and been able to get them running just by getting all of the routers timed at the same time. I have done it just by setting it up on my R1 router, copy the command I just put in and paste it into the others. It only put the routers off by a few seconds and then my neighborships formed after I changes the times on there.
Strange that it would not do it for you unless there are some of the interface commands being missed on some of the other routers. I believe some others have suggested to verify that as well.
Thank you Ahmed and everyone for mentioning that NTP needed to be setup on the routers. I struggled for 2 days beating my head against the wall on this issue. After reading this post, I configured NTP on my routers and EIGRP Authentication finally started working!!!
R1#show ip eigrp int detail
IP-EIGRP interfaces for process 10
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0 1 0/0 56 10/380 640 0
Hello interval is 2 sec
Next xmit serial <none>
Un/reliable mcasts: 0/0 Un/reliable ucasts: 27/30
Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 4
Retransmissions sent: 0 Out-of-sequence rcvd: 1
Authentication mode is md5, key-chain is "EIGRP_KEYS"