Configure smaller cache lenght (duration) and change it to "seconds", not minutes.

I would like to change default hardcoded cache to 30 seconds.
define ('TWITTER_PULL_CACHE_LENGTH', 20); //-- cache for 20 minutes
to
define ('TWITTER_PULL_CACHE_LENGTH', 30); //-- cache for 30 seconds

AND

$cache_length = twitter_pull_cache_length() * 60; //-- in the settings we indicate length in minutes, here we need seconds.

to

$cache_length = twitter_pull_cache_length(); //-- in the settings we indicate length in SECONDS

How can it be done in template.php?