Plan daily tasks by priority.
Daily task lists are almost always longer than the day. Discounting available focus time for interruptions — typically a quarter of it in an open working environment — and dividing by average task length gives the number of tasks that actually fit. The overflow figure is the useful one: it tells you how many items to move or drop deliberately at the start of the day rather than by default at the end.
Achievable task count
Effective minutes = focus hours x 60 x (1 - interruption share); tasks achievable = floor(effective minutes / average task minutes); overflow = list length - achievable
Because lists are built from what needs doing and days are bounded by time. A fourteen-task list at 25 minutes each is nearly six hours of pure execution, which exceeds the effective focus time in almost any real working day.
Twenty to thirty percent in a typical office or remote-with-messaging environment, and considerably higher in support or management roles where responsiveness is the job.
By importance, before the day starts. Left to itself, the overflow is whatever was at the bottom of the list, which correlates with nothing useful. Deciding in advance is the entire value of the calculation.