Yes. CGI processes and individual ssh commands are limited to two to five minutes of CPU time, and PHP requests are limited to three minutes of wall-clock time by default.
These restrictions are designed to catch runaway processes, not to interfere with ordinary usage. "Stock" web applications, specifically including phpBB and WordPress, simply do not use enough resources to encounter these limits. Who would wait three minutes for a web page to load anyway?
If you have a need for longer-running processes (e.g. for non-interactive use), there is usually a way to make that work or adjust our system settings to accommodate it.
Although we do not impose an overall specific per-site CPU limit, ours is a shared hosting service. We try to accommodate individual needs, particularly on plans where you pay for the resources you use, but we do reserve that right (and responsibility) to limit anything that causes disruption to others. If you have a site on one of our older plans that does not include a resource-billing component, attempts to use large amounts of resources are more likely to encounter limits depending on total available resources.