One technique you could use is to set an alarm. Consider:

use strict;
use warnings;

waitForSomeTime ();


sub waitForSomeTime {
    my $bail;

    local $SIG{ALRM} = sub {$bail = 1};
    alarm 5; # Bail in 5 seconds if we don't stop beforehand

    while (! $bail) {
        # Do stuff in here that might terminate the loop
        # but don't use sleep() because alarm may get grumpy
    }

    if ($bail) {
        print "Must have bailed\n";
    } else {
        alarm 0; # Reset the alarm
        print "Loop terminated some other how\n";
    }
}
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