Because it was already very late after solving the case, Hattori and Heiji were not in a hurry to go home. Instead, they planned to stay at Karasawa's house for another night and then return to Kansai early the next morning.
"After all, it's another matter whether I can buy a ticket to go back at this time. It's already late at night when I go back, and there's nothing urgent tomorrow, so naturally