I would say for both AB and LH it very much depends on how many flights depart from the airport. If they have a substantial number of flights, they are likely to staff a permanent desk (or more likely contract a ground handling agent to do so). If it is just the one flight, both will have rather limited hours. For instance at NAP also AB had a desk which was open for a number of flights and thus more than 2 hrs before (at least for my flight, which wasn't the first to depart).