Your problem is that (syntactically speaking) your slice happens before you get a chance to dereference.

Try adding braces, like this:

%x = (
  abc => { ip => v1.2.3.4, last_time => 'today' },
  def => { ip => v5.6.7.8, last_time => 'yesterday ' },
);

@y = @{$x{def}}{'last_time', 'ip'};
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