"A few hours?" shrugs Asmodia. "Once I cast it, it just kind of stays that way for a while unless I make it stop."

It doesn't occur to her that it might require particular effort to sustain this spell. Most spells don't really need anything from their caster after the initial work of making them happen. "I can't really split it, though, so we'd need a fire if you didn't want to hang around with me."