[SOLVED]How to measure program execution time in Linux

#/opt/script/mil-of-files.sh
#KET QUA CHINH XAC DEN PHAN NGHIN GIAY
####################
now="$(date +'%Y.%m.%d-%H.%M.%S.%3N')"
now1="$(date +'%Y.%m.%d-%H.%M.%S.%3N')"
start_ts="$(date +'%s%3N')"
#############COMMAND:BEGIN
#PLACE YOUR COMMAND HERE

#############COMMAND:END
now2="$(date +'%Y.%m.%d-%H.%M.%S.%3N')"
stop_ts="$(date +'%s%3N')"
DIFF=$((stop_ts-start_ts))
hour=$((DIFF/(60*60*1000)))
min=$((DIFF/(60*1000)))
sec=$(((DIFF%(60*1000))/1000))
ms=$(((DIFF%(60*1000))%1000))
echo "####################################"
echo "**RUNTIME**|[""${hour}:${min}:${sec}.$ms""](h:m:s:msec)"
echo "STARTING...|"$now1
echo "...... DONE|"$now2
echo "####################################"

#RESULT:
# ####################################
# **RUNTIME**|[0:1:26.501](h:m:s:msec)
# STARTING...|2015.09.25-14.08.01.327
# ...... DONE|2015.09.25-14.09.27.828
# ####################################