Josh informs Isla that he will be out of detention at 6 PM on Saturday and is willing to meet her anytime afterward. He seems eager to see her and is open to her choosing the meeting spot, showing his flexibility.
He also hints that because Isla asked him out, it is her responsibility to pick the place, and he assures her that whatever she suggests, he will agree to. This encourages Isla to feel confident in planning their meet-up without worry about rejection.