online appointments PHC part 2

I need an app that clients can download on their mobiles. Clients need to be able to cancel their own appt and re-make their new appt. i need for there always to be only 3 possible appointments to be shown in chronological order. The reason is; i don’t want, for example, 3 appointments in a row and then 2 hours later the next appointment. Staff cannot be waiting with nothing to do for an hour or multiple hours. After you have checked it and KNOW that you can do the job, Bid on it.