When SSLSessionCacheTimeout is set to a value less than or equal to 3600, and SSLVerifyClient is set to true, the log shows that the interval between mod_ssl's verifying the client certificate is the value of SSLSessionCacheTimeout. When it is set to 5400 or lager, mod_ssl still verifies the client certificate every 3600 seconds. In addition, SSLSessionCacheTimeout defined in virtual host doesn't overwrite the value defined in ssl.conf.