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