I have generally written a log file to keep track of the performance of my scripts. For example
echo Starting data mirror >> /quitelarge/_mirror/mirror.log
echo $(date +%y/%m/%d_%r) >> /quitelarge/_mirror/mirror.log
I also write and entry to the log when major milestones in the process complete - same syntax.
Hope this helps.
p.s. these lines are included in the shell script which would be executed by cron.