TGI is right on about avoiding sleep. However, since you are a beginner, I will say to use a "repeat" statement, instead of an "after". Essentially, they are the same thing, but repeat is a bit clearer for repetitive things, whearas after is usually used for a 1 time delay.

my $repeater = $mw->repeat( $update_rate, \&Refresh, $somedata);
#later to stop it
$repeater->cancel
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