You can use using_wait_time(seconds) method like:
using_wait_time 3 do
expect(page).to have_text 'Lorem ipsum'
end
or :wait option (that appeared in Capybara 2.1).
Note that :wait option was supported only by find method in Capybara 2.1.
Support for :wait option in matchers (i.e. has_x? and have_x methods) has been added in Capybara 2.2:
expect(page).to have_text('Lorem ipsum', wait: 3)