s your time offset units your time reference date is adjusted
accordingly without too much further effort to ensure anything
about it (in the hope that <code>mktime(3)</code> will take care of this later).
This may lead to some surprising (or even invalid!) results,
e.g. 'May&nbsp;31&nbsp;-1month' = 'Apr&nbsp;31' (meaningless) = 'May&nbsp;1'
(after <code>mktime(3)</code> normalization); in the EET timezone
'3:30am Mar 29 1999 -1 day' yields '3:30am Mar 28 1999' (Sunday)
which is an invalid time/date combina