Concerto: I think that's easily do-able. But, bear in mind that LCY doesn't recognize 'connecting flights' as such! You'll have to disembark, come out into the (landside) check-in hall and then go back through security. But, assuming your onward from LCY is a domestic AF (CityJet) flight, then they actually allow check-in up to 10 minutes before departure! And, if you're already checked-in (online), then you should have no problem at all (assuming your inbound is reasonably on-time). You should even have time to get your shoes shined and indulge in a pot of wasabi peas!

-- Henry