He replies hours later every time. Is that a sign?
A reply after several hours may be too slow for what you need, without being a measure of your place in someone's life. An urgent practical question and a casual conversation also need different response times.
The useful agreement is about those needs, not matching his delay minute for minute. A reply expectation can be discussed directly, with room for each person's schedule and an honest answer about what is realistic.
The line you can send
I don't expect instant replies, but time-sensitive plans are getting difficult. What timing works for you?
Yours will sound different
Bring the message you keep rereading. The first reads are free, and nothing is sent to him.
Ask about mine