Conditional functions by date

Yes it is. You can use timetamp values (from the date() function) or time objects (new DateTime()). YOu can use both of these in calculations or comparisons.

Please, can you show me an example as a conditional?

Something like this?

$now = current_time ();
$then = strtotime( '2017-08-19' );

if( $now < $then ) {
    echo "It's before the time";
}
else {
    echo "It's after the time";
}