How to correctly add a duration to not have it result in invalid date?

Last night abou 2:15am we had some automated tests fail with this error:

Invalid local time for date in time zone: America/Los_Angeles


The problem was that (for some reason) we had a duration object of ( years
=> 7, days => 1 ) which we added to DateTime->now which ended up March 8,
2020 which is a DST change -- and 2:15am does not exist in that time zone
on that date.

If $dt and $duration can be anything, what's the best way to prevent adding
a $duration to a $dt and having it land on a non-existent date?

I realize that durations are a bit ambiguous, but is it reasonable to write
something like

     $expires_time = $start_time->clone->add( days => $expire_days );  # or
even ( years => 7, days => 1 ) like above

and not have it throw an exception?   I suspect most of us expect (and
hope) that $expires_days in the future will exist.   Or should we always
write:

$dt->add( hours => $expires_days * 24 );


What would happen if duration calculations were always done in UTC?

$tz = $dt->time_zone;
$dt->set_time_zone( 'UTC' );
$dt += $duration;
$dt->set_time_zone( $tz );



 What advice should I give to our developers about adding durations safely?
   It's a common operaton in our apps.

Thanks,

-- 
Bill Moseley
[email protected]