Very interesting.

When we colonize other planets the conversion-rates would be static due to longer or shorter days. Of course assuming that value of time depends on the length of a day.

You would have to consider the age, as one hour for a child is experienced as faster than an old mans.
And not to mention as the social cultures and technology is so rapidly changing, old hours would be less valuable compared to new. The new hours would be more efficient due to better tools.