int time(time_t timeptr)
The number of seconds since January 1, 1970 12:00:00 GMT (also known as the [Unix Epoch]).
Returns the current time as expressed in seconds since the Unix Epoch.
You can find the number of days since the Unix Epoch by dividing the answer by 86400. (60 seconds * 60 minutes * 24 hours = 86400 seconds in a day.)
It's possible that the first parameter of the time function can take a pointer to a data structure - the time function in C allows passing a pointer to a time_t structure/object. However, since FilterMeister does not yet support the time_t type, the author of this documentation has assumed that the first parameter given to time must always be NULL.