Especially following points:

-        One day has 24 hours

-        One hour has 60 minutes

-        One minute has 60 seconds

-        To increase accuracy, seconds are splitted in decimal system (ex: 24.86 seconds)

-        One week has 7 days

-        On month can have either 28,29,30 or 31 days

-        One month can have anywhere between 4.0 weeks and 4.4 weeks

-        Months start and end on different days of the week

-        In one year can be 365 or 366 days

-        Leap year is every 4th year

-        Date is counted as “ongoing” system as opposed to time that counts “time past” system.

For example: on the first day of the year the date is already 1/1 even though 0 full months have passed. The same is true for the ongoing year. As opposed to time, where the first hour of the day is 0. The same for birthday dates, the first year will be 0 because 0 of full years passed since the birthday, and it counts only in months.

-        New day starts in the middle of the night

-        New year starts in the middle of the winter (or summer)

-        One day has 2 full rounds on the clock. That may lead to confusion between AM and PM

Inconvenience:

-        The conversion between time frame units [months, weeks, days, hours, minutes, seconds] is not trivial.

-        Lots of different formats for date representation. This Leads to confusion. Most of them are difficult to sort in the digital world

-        It’s difficult to count days (or hours) between two dates

-        It’s difficult to learn the system

-        “Time past” system is a more natural way to count date-time than an “ongoing” system

-        It’s not easy to remember when the leap year will be.