$ strings `which date` | grep '%s'
$
Returns nothing
$ which date
/usr/bin/date
$

Here is the code I have been testing with:
#!/bin/ksh
start=$(date +%s)
time sleep 20
end=$(date +%s)
echo "Time: $((end - start)) secs."

Results: syntax error

changed to:
#!/bin/ksh
start=$SECONDS
time sleep 20
end=$SECONDS
echo "Time: $((end - start)) secs."

Results: This works!

My question now is, will it still work after hours of execution. How ofter does this value get reset?