On the Zend Developer Zone there's a recent post about a custom filter that's been developed to help filter events based on time instead of just logging them as a whole.
For one of my recent project, which is using Zend_Log component of the Zend Framework, I had a demand in which I needed to be able to filter log events based on the time they occurred. As out of the box, Zend_Log component does not have such filter, I decided to create one that will fulfill my demands.
The log filter, NP_Log_Filter_Timestamp, it allows you to set rules for things like hour, minute year, day of the week, etc. and can be used anywhere you'd create a normal Zend_Log instance. Pass it in the format you'd like to use (that idate can use), a value to evaluate and a comparison operator. Two code snippets show how it's used.