Accepts following formats
1. String "now" refers to current time
2. A sequences of digits, like "123456890"
(indicating the time in seconds after the epoch)
3. A string like "2002-01-25T07:00:00+02:00" in datetime format
4. A number followed by one of the characters s, m, h, D, W, M, or Y
(indicating seconds, minutes, hours, days, weeks, months,
or years respectively), or a series of such pairs.
In this case the string refers to the time that preceded
the current time by the length of the interval.
For instance, "1h78m" indicates the time that was
one hour and 78 minutes ago.
5. A date format of the form YYYY/MM/DD, YYYY-MM-DD, MM/DD/YYYY,
or MM-DD-YYYY, which indicates midnight on the day in question,
relative to the current time zone settings.