If you do not have any policy-map applied that changes the UDP/123 timeouts, it might be a bug.
CSCso29047 Bug Details
set random-seq-number disable in MPC affects on UDP/ICMP conn timeout
Symptom:When random-sequence-number is disabled in policy-map, this causes the UDP connection timeout set to 60 minutes when global timeout for UDP/ ICMP is set to two minutes.Conditions:Random-sequence-number is disabled in policy-map.Workaround:Do not disable random-sequence-number feature
If this is not the case, you can try opening a TAC case.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...