The problem is that we are dealing with very arbitratry yet very important values, the day and the year. This means we will have to make some arbitrary decisions while making a time measurement system, rather than being able to base everything off the Planck time.

We could, of course, divide up the day metrically (preferrably after we switch to dozenal for divisibility) and skip months entirely to minimise irregularity, but the current system is so deeply rooted in our culture and so difficult to replace satisfacorily that I still expect to have to endure it for a very long time.