Ed. Note: Ewald Wuschke wrote this in response to my deletion of the Timely plugin and is great advice for managing plugins on any site.
I can sympathize with the issues some plug-ins (especially free versions) can create with website Content Management Systems such as WordPress and Joomla. It can take many hours, if not weeks, to try to resolve.
A while back, I needed to experiment with a room booking system for our church's website. The website is based on Joomla, not WordPress. I installed a plug-in component called "Scheduler" and encountered multiple conflicts that caused the website to break.
The solution was to create a separate Joomla website within a new subdomain, where the only plug-in installed was "Scheduler". The new website used a much more up-to-date version of Joomla compared to the church's main website which worked better with "Scheduler". To go to the "Scheduler" site, one simply has a link from the main church webpage; on the "Scheduler" site there is a link to return to the main church webpage. The beauty of having a separate website, is that when one decides not to use "Scheduler" anymore, one can delete the website and its database without affecting the main website and database. It also means that the main website is not affected by any bugs that may arise while using the plug-in. The two websites are independent of each other, just "connected" by links.