What to text when he takes hours to respond every single time

Before you send anything back, notice what consistent slowness tells you. It's not a mystery. He's had hours to respond and chose not to until now. That's data. He might have a legitimate reason, but the fact remains that you are not a priority message right now. You need to treat this as information about where you stand, not as a personal failing or a challenge to overcome. Your job is not to figure out how to make him respond faster. Your job is to decide if you want to keep texting someone who operates on this timeline. Matching his energy is fine. Chasing it is not.

When someone responds slowly, longer messages backfire. A detailed text or a question that needs thought just sits there for another few hours while he decides it's too much effort. Short, simple messages are easier to reply to, which removes the friction he might already feel. You also want to avoid questions that require him to carry the conversation. Ask something, but leave room for him to give a one word answer. Better yet, make a statement that he can respond to casually. The point is to not make his slow response feel worse by dumping a lot onto him.

Don't time your message around his pattern. Don't send it at 2am hoping he'll see it first thing. Don't send it during work hours guessing when he'll check his phone. Send it when you naturally would, then move on with your day. After you hit send, do not check your phone constantly. Do not send a follow-up message. If he responds in an hour, great. If he responds tomorrow, that's the baseline you now know. After three or four message exchanges where he consistently takes hours, you have enough information. At that point, stop initiating. Let him reach out and see if his response time changes when he's the one starting. If it doesn't, you have your answer.