One way would be to switch to PowerShell.
$path = '\\server\path'
$filter = '*.bak'
$retentionDate= (Get-Date).AddHours(-12)
#################################################
Get-ChildItem (Join-Path $path $filter) -Recurse |? {($_.PSIsContainer -eq $false) -and ($_.LastWriteTime -lt $retentionDate)} | Remove-Item -WhatIf
Just remove the -WhatIf from the code when you're ready for it to do work.
There are no special teachers of virtue, because virtue is taught by the whole community.
--Plato