Hi Praveen,
You forgot to mention error you are getting.
Any ways you can get date difference easily in BODS using in built function.
Date_Diff.
Please see attached pic.
its there in reference guide. on page no.788.
What you can do is instead of getting only time portion you can create two variable to store complete date.
like
$var1 = sysdate() ; in your first script.
$var2 = sysdate(); in your second script
And in third script you can apply function like
$diff_hour = date_diff($var1,$var2,'H')
$diff_minute = date_diff($var1,$var2,'M')
& then final_diff = $diff_hour || $diff_mintue.
THanks,
Swapnil