We are importing this way(before it is needed, not at the beginning of the app) in our WebQA projects and also in all the other app objects in gaia-ui-tests.
Examples:
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/clock/app.py#L69
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/clock/app.py#L99
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/contacts/app.py#L38
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/contacts/app.py#L43
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/contacts/app.py#L66
https://github.com/mozilla/gaia-ui-tests/blob/master/gaiatest/apps/gallery/app.py#L31

I would prefer we keep the code consistent.