bat 语句 怎么计算两个时间差

@echo off
echo 现在时间是%time:~0,2%点%time:~3,2%分%time:~6,2%秒
set time1=%time:~0,2%%time:~3,2%%time:~6,2%
pause
echo 现在时间是%time:~0,2%点%time:~3,2%分%time:~6,2%秒
set time2=%time:~0,2%%time:~3,2%%time:~6,2%

set /a time3=%time2%-%time1%
echo 间隔%time3%秒
pause

来源：http://zhidao.baidu.com/question/195532840.html