you can simplify it a bit replacing the eval "..." by a eval {...} and returning a reference to Time::HiRes::time instead of it wrapped inside an additional sub:

package P;

sub new {
    my $class = shift;
    my $self = {};

    $self->{_time_func} =
      eval { require Time::HiRes }
        ? \&Time::HiRes::time
        : sub { time() };

    bless $self, $class
}
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