I apologize if this has been asked in the past, but I searched and could not locate it.
In Lion & Dragon, how long is a demon summoned for, assuming it is dominated successfully? We've been playing that it's only summoned to complete some specific task and then it returns to Hell.
That's correct. When you summon a demon, it is for the purpose of fulfilling a single task. The demon may do the task itself, or may send secondary demon(s) to do it, or use some power, or grant the PC some knowledge, whatever is actually reasonably necessary to do the task.
The effect lasts until the task is fulfilled, or it becomes impossible for the task to be fulfilled, or the demon (or subsidiary demons) sent to do the task are banished/destroyed, or until the summoner bids the demon/subsidiaries to depart.
Thank you.