ts_to_ct messages; ntp: time correction of -1200 seconds exceeds sanity limit

FreeBSD gohorns.x 9.0-CURRENT FreeBSD 9.0-CURRENT #1 r216088: Thu Dec  2
23:20:14 CST 2010     root_at_gohorns.x:/usr/obj/usr/src/sys/GENERIC  amd64

I have been getting a lot of ts_to_ct for months: are we supposed to
look for something or report anything about these?

 I just noticed an NTP error in /var/log/messages:
...
Dec  4 02:52:18 gohorns kernel: ts_to_ct(1291431138.717914676) =
[2010-12-04 02:52:18]
Dec  4 03:09:05 gohorns ntpd[1934]: time reset +2.018106 s
Dec  4 03:09:05 gohorns kernel: ts_to_ct(1291432145.779273676) =
[2010-12-04 03:09:05]
Dec  4 03:11:40 gohorns kernel: ts_to_ct(1291432301.024288164) =
[2010-12-04 03:11:41]
Dec  4 03:45:36 gohorns ntpd[1934]: time reset +1.976613 s
Dec  4 03:45:36 gohorns kernel: ts_to_ct(1291434336.662385061) =
[2010-12-04 03:45:36]
Dec  4 03:45:36 gohorns ntpd[1934]: kernel time sync status change 6001
Dec  4 03:45:36 gohorns kernel: ts_to_ct(1291434336.712917848) =
[2010-12-04 03:45:36]
Dec  4 03:46:38 gohorns ntpd[1934]: time correction of -1200 seconds
exceeds sanity limit (1000); set clock manually to the correct UTC time.
Dec  4 04:15:36 gohorns kernel: ts_to_ct(1291436136.712892982) =
[2010-12-04 04:15:36]
Dec  4 04:45:36 gohorns kernel: ts_to_ct(1291437936.712891437) =
[2010-12-04 04:45:36]
Dec  4 05:15:36 gohorns kernel: ts_to_ct(1291439736.712890731) =
[2010-12-04 05:15:36]
...

At "Sun Dec  5 19:56:19 CST 2010" according to other systems, this
machine says the time is

gohorns:/root# date
Sun Dec  5 20:11:01 CST 2010
gohorns:/root#

Has anyone seen anything like this?  Suggestions on what to look for as
a cause?

The system is a Dell Zino HD, dmesg:

CPU: AMD Athlon(tm) Neo X2 Dual Core Processor 6850e (1800.10-MHz
K8-class CPU)
  Origin = "AuthenticAMD"  Id = 0x60fb2  Family = f  Model = 6b 
Stepping = 2
 
Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
  Features2=0x2001<SSE3,CX16>
  AMD Features=0xea500800<SYSCALL,NX,MMX+,FFXSR,RDTSCP,LM,3DNow!+,3DNow!>
  AMD Features2=0x11f<LAHF,CMP,SVM,ExtAPIC,CR8,Prefetch>
  TSC: P-state invariant