The #CACHE{time in seconds} tag is used to determine the time period which will pass before the template is freshly recalculated [1]. The time is expressed in seconds. It may be specified as a calculation.
This tag is generally inserted right at the start of template files. In its absence, by default, the period is set at 24 hours (as defined by the _DUREE_CACHE_DEFAUT constant).
For example:
#CACHE{24*3600*30}
would mean that your template file is refreshed every month (30 days).