Terminate program if execution time is longer in command line

Question

I write the code as following in batch file

@echo off
cd c:\temp
set st = %TIME%
loop
set et = %TIME%
if %st% - %et% > 1000(taskkill /f /im loop.exe)

but in this code, if program loop (loop.exe) loops forever, command after loop command never will be reached. What can I do? Please help!