I think you'll find the error right about here ...

$t = timeit(1, \&stuff(1000000));
               ^
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You're trying to execute a reference that points to the return of the stuff sub. Instead you probably want something like this

$t = timeit(1, sub { stuff(1000000) });
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If you want to time functions within programs you may also want to check out the Devel::DProf module.
HTH

_________
broquaint