If your computer is running ntpd and you have usb networking, you can ssh to your kindle and get the time from your computer.
Code:
ssh root@192.168.15.244
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# N O T I C E * N O T I C E * N O T I C E #
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Rootfs is mounted read-only. Invoke mntroot rw to
switch back to a writable rootfs.
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[root@kindle root]# ntpdate 192.168.15.201
29 Dec 15:24:41 ntpdate[16285]: step time server 192.168.15.201 offset 16.067199 sec
(Use different IP addresses if you changed defaults)