Who most likely are the speakers?

M: Hi, this is Mike calling from Parker’s Dentistry to confirm your appointment for tomorrow morning at 9: 00 a. m. with Dr Parker.
W: Thank you for reminding me. Actually, I do need to change the time of my appointment. I have a schedule conflict. And I can’t make it that early.
M: That’s alright. I think I should be able to make it at 4: 00 p. m. Would it be a better time?
W: No problem. Thanks a lot.