[SalesForce] How to query the data that has been modified in last 24 hours

This will Select correctly based on the question above, hope this helps someone else. Cheers.

SELECT 
        Id, 
        LastModifiedDate,
  (
    SELECT 
            Id, 
            CreatedDate

    FROM FeedComments 

    ORDER BY CreatedDate ASC
  )

FROM UserFeed

WHERE (
            (
              ParentId = {$this->uid}
            )

        AND (
              LastModifiedDate > {$this->lastModStamp}
            )
      )

OR    (
            (
              CommentCount > 0 
            )

        AND (
              CreatedDate > {$this->lastModStamp} 
            )
      )

ORDER BY CreatedDate DESC;

A good way to test this is to flip the

OR ((CreatedDate > YESTERDAY) AND (CommentCount > 0))

to

OR ((CreatedDate < YESTERDAY) AND (CommentCount > 0))

and use something like this to run through it

        header('Content-Type: text/plain');

        $query      = str_replace('{/id}', "'".SF_UID."'", $_POST['q']);
        $response   = $mySforceConnection->query($query);
        $sResult    = New QueryResult($response);

        $i=0;
        foreach ($sResult as $splObject)
        {
            echo "ID: {$sResult->records[$i++]->Id[0]}\n";
            print_r($splObject->fields);
            echo "\n\n";

            if (is_array($splObject->queryResult))
            { 


                $fResult    = New QueryResult($splObject->queryResult[0]);
                $j=0;

                echo "\n---------------------------------------------\n";
                foreach ($fResult as $fplObject)
                {
                    echo "ID: {$fResult->records[$j++]->Id[0]}\n";
                    print_r($fplObject->fields);
                    echo "\n\n";
                }
                echo "\n\n\n\n\n\n";
            }
        }
    }

When trying to sync, you don't need to worry about the mechanics of determining the correct time to use. Instead, just use getUpdated (/vXX.X/sobjects/ObjectName/updated?start=X&end=Y in the REST API), which will return a list of ID values you can retrieve from and a value called lastDateCovered, which is the next start time that you should use in your replication. In flight requests won't be included, but the lastDateCovered attribute will be offset by any in flight requests-- your next sync request will automatically include any values you missed in the last request because they were still in flight (not fully committed). The only issue you have to worry about is selecting the correct first initial sync date/time. For more information, I'd suggest taking a look at the SOAP API Developer's Guide under Data Replication, and the Force.com REST API Developer's Guide for REST-specific considerations.