any easy way to find post for today and yesterday...

softech it is possible by using the custom FreeMarker context object datesupport that Khoros provides, that will allow you to do something like this:

${datesupport.now.addDay(-1).date?datetime?iso_utc}

<#assign 24hoursago = datesupport.now.addDay(-1).date?datetime?iso_utc />
<#assign query = "SELECT * FROM messages WHERE post_date > ${24hoursago}" />