All dates in the Stack Exchange API are in unix epoch time, which is the number of seconds since midnight UTC January 1st, 1970. The Stack Exchange API does not accept or return fractional times, everything should be rounded to the nearest whole second.
todate parameters are accepted by many methods, and are always dates.
parameters may accept dates, depending on the
For convenience when doing ad-hoc queries without a
key an alternative date format is accepted:
YYYY-MM-DD HH:MM:SS, where
the hour, minute, and second values are optional. Applications should not ship using this date format (as all applications should ship with a key), it is provided just to ease rapid development.
All dates returned by the API are in properties ending
_date. The documentation console indicates these with , hovering
over them will show a human readable version.