If the timer activates a bit early then a task might be just a few
seconds short of being allowed to run. This would run such a task rather
than wait another hour.
The value 0.5% chosen so that a weekly task does not run an entire hour
earlier than last time.
Eventually the goal is to have daily tasks run while there is little
activity, but that will vary with the server and the usage patterns of
its users. This is a start anyway.
A number of modules now have periodic tasks that need to run, e.g. for
cleaning out old messages or files. This has highlighted a need for
coordinating and optimizing scheduling of such tasks.
