 an <em>amount</em>. The following time units can be
used to specify the <em>amount</em>: <strong>years</strong>, <strong>months</strong>, <strong>weeks</strong>, <strong>days</strong>,
<strong>hours</strong>, <strong>minutes</strong>, or <strong>seconds</strong>. These units can be used in
singular or plural form, and abbreviated naturally or to a single
letter (e.g. +3days, -1wk, -3y). Several time units can be combined
(e.g., -5mon1w2d) or concatenated (e.g., -5h45min = -5h-45min =
-6h+15min = -7h+1h30m-