“I’d love to get your next appointment on the calendar before you head out — it saves us both the texting back and forth, and it means you’ll always get the day and time you want.”
Then make it a recommendation, not a question mark: “For your hair, I’d want to see you in about six weeks — that keeps this shape exactly where we want it. Does the same day and time work?”
If they hesitate, keep the door open: “No pressure — I can pencil it in and we’ll confirm the week before.” A penciled date beats no date every time.