here's part of the code that causes the problem:

if(isset($timer)) $four=$timer->get();

    if( !empty( $ev->repeat_id) )
        printf( "&REPEAT_ID=%s", $ev->repeat_id);
    if(!empty($end_date)) print "&END_DATE=$end_date";

if(isset($timer)) $five=$timer->get();


Produces the following timings:
four=3.0422940254211, five=3.4876440763474

Interestingly, this is repeatable many times through several different pages, but in different sections of code (all seemingly innocuous and they definitely 'behave' correctly most of the time, e.g. 1 time out of 15 in a loop on the same page the above code will give that slow response, the other times it will execute quickly):
four=4.3863810300827, five=4.3864229917526

Other info (sorry, I don't think I can give you a small script).
Configure line:
 './configure' '--prefix=/opt/local/packages/php-4.1.1' '--with-jpeg-dir=/opt/local/' '--with-png-dir=/opt/local/' '--with-zlib-dir=/opt/local/' '--with-xpm-dir=/opt/local/' '--with-imap=/src/archive/i/imaped/imap-2001a' '--enable-inline-optimization' '--enable-bcmath' '--enable-calendar' '--with-regex=system' '--with-apache=/src/archive/a/apache/prod_build/apache_1.3.23' '--with-ftp' '--with-oracle' '--with-oci8=/opt/local/packages/oracle-9.0.1' '--with-snmp=/opt/local/' '--with-yp' '--enable-ucd-snmp-hack' '--with-openssl' '--with-config-file-path=/local/etc/httpd/' '--enable-safe-mode' '--enable-track-vars' '--enable-trans-sid' '--enable-magic-quotes' '--with-gd=/opt/local/' '--enable-gd-imgstrttf' '--enable-xml'