He didn't really know exactly. James had thought she would be back by now, so he didn't feel qualified to estimate a time further than 'soon' or 'any minute now.' Luckily, the greasy-haired boy apparently decided to leave anyway. James couldn't rise fast enough to see him out of the house, now that the end was in sight.
"Are you sure?" he asked, and then left only a brief gap before adding. "Okay. I'll let her know you called by."
James followed Severus to the door to see him out, not really having anything else to say himself.