They cannot do this no matter what time his trip ends. He is still a REG pilot at the end of that trip thus has no required schedule check and no way to be notified of any rest until he starts LC at midnight. Assuming they call him right at 0001 and he’s smart and doesn’t answer the phone the earliest rest could start is 0201. They can stitch X day and pre-CQ rest together as long as it is done and notified in advance. So if he’s got a C period day one then they’ve got a small window starting at 0001 01OCT to hit him with a rest assignment. But regardless even if they do I’ve never heard of anyone getting hit with a turn post-1800 on a single reserve day. Like you said it is technically possible but extraordinarily unlikely. Even if such a short turn did pop up it’d probably be grabbed as a WS.