Sounds like a job for SQLAgent. You can check for the last update and if it's not within your time frame, use xp_sendmail to fire off the email. Or, when you write to the log you could update another table consisting of a single row. Check the time there. It should be loads faster than hitting the log table.
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/shop/product.asp?ProductID=NI-SQL1
K. Brian Kelley
@kbriankelley