Source

File: wp-admin/includes/class-wp-filesystem-direct.php

public function touch( $file, $time = 0, $atime = 0 ) {
		if ( 0 == $time ) {
			$time = time();
		}

		if ( 0 == $atime ) {
			$atime = time();
		}

		return touch( $file, $time, $atime );
	}