Clients eh?! Lol this happens to me all the time with people wanting to book appointments or book a course. What I have done now is written a generic reply and if needs be I send them that. Seems to work and also makes them feel a little bit guilty haha! This is what I send:
Hi, thank you so much for your enquiry. Unfortunately I am currently unavailable as today is my day off. Please bear with me and I will reply as soon as possible when I return to work. Thank you again for your message and I look forward to speaking to you soon, kind regards, Jody (Fingers n Toes)