I used `RSpec::Core::Time` to be internally consistent with how the time gets calculated inside of `Example`. In the unlikely case of us changing how `RSpec::Core::Time` works, this spec might get re-examined because it uses it, which is probably a good thing.

I chose 0.5 so that I wouldn't have to change the specs expecting output like this:

```ruby
expect(output.string).to match(/0(\.\d+)? seconds/)
```