The prop and evar values are read in as Strings by AA. Hence it is impossible to create a segment treating the values as dates. Also, the format for dates keep changing (YYYY-MM-DD, DD/MM/YYY, MM/DD/YYYY, etc), so it is hard to convert the strings to dates.
For the questions regarding capturing Days of week, hour of day, etc, you may want to have a look at getTimeParting plugin.
There are also several time dimensions now available, which can be used to create a segment (not the prop value)