There is a sudo random number generated in a command line shell you can call timeout /t %random% however there is no way to control the value range which is a 32 bit int. You'd have to do some math to control the value to get a range of 5-30 minutes.
If you re-wrote the batch file into a Powershell script it's much easier to control that timing.
<command one>
$wait_time = Get-Random -Minimum 300 -Maximum 1800
Start-Sleep -Seconds $wait_time
<command two>