PowerShell Need leading zero

Problem:
SET Today=%date:~4,2%%date:~7,2%%date:~10,4%%time:~0,2%%time:~3,2%%time:~6,5%.log
 echo %today%

If you run above script, you will get space, if the system time is AM.
Solution:
set hour=%time: =0%
SET Today=%date:~-4%%date:~4,2%%date:~7,2%_%hour:~0,2%%time:~3,2%%time:~6,2%.log
echo %Today%