Corrections:

1. ps -p 1 -o etime | tail -1 will give the system uptime time in format "day-hour:minute:second"
2. Use timelocal in module Time::Local to convert the current timesystem uptime to seconds since EPOCH
3. Value from 2time() minus Value from 12 should give me the EPOCH time of last system reboot
4. Value from 3 plus first column in dtrace script output divided by 1000000 should give the EPOCH time of the record
5. localtime(Value 4) should display it in readable local time format.

If you could get the reboot time directly, you'd get more precise results.