I'm assuming that the date/time of the log entry is being written to the database, and I also assume that you only want the last record added to the table, so try this:
WHERE logfile = 'Microsoft-Windows-PrintService/Operational'
AND EventIdentifier IN (307,800)
ORDER BY datetimefield DESC;
Finally, in the code snippet I provided, I use
because I don't know what the name of your column is.
BTW, your logic is kinda screwed up (or you're just not expressing yourself very well). You can't retrieve data newer than the last data written to the db because it's never going to be there.