I've tried to 'port' your Timer plugin to my Forums instalation... Have you tried this? I created the plugin, added the PRE and POST hooks correctly (search results hook name changes in Forums to do_search_results) also small changes to the code were neccesary, however I receive the following message:
Can't use string ("search_results.html") as a HASH ref while "strict refs"
Any idea why this is happening? It looks to me it is related to a template exporting thing because in YOUR original code you export $TPL which, I Assume stands for template.. in GForum I can not export it..