checkdate() — Validate a Gregorian date
date() / gmdate() — Format a local/GMT time/date
getdate() — Get date/time information (from a timestamp)
gettimeofday() — Get current time (as an array)
localtime() — Get the local time (as an array)
mktime() / gmmktime() — Get Unix timestamp for a date
strftime() / gmstrftime() — Format a local/GMT time/date according to locale settings
strtotime() — Parse about any English textual datetime description into a Unix timestamp