In PPS Express you can control your availability via the Settings screen.
Once here choose Diary Options. From here you'll be able to control the diary availability for the user you are logged in as. Verify that this is the correct person by checking the "Diary Set up for..." section. If you wish to adjust another user's availability then you would need to log in to PPS Express as them.
Here you'll find availability settings for each day of the week. To begin, tick the box beside each day to enable that day. You can then determine the availability duration in the From and To field and set your Appointment Duration. This is the default slot allocated for each appointment but you can alter this at the point of booking for each appointment.
You can set up availability as on session for your full working day or as a series of sessions using the Additional Sessions options. For example, you may set up your morning sessions each day of 9am - 12:30pm and then open an Additional Session option to add your afternoon sessions of 1pm-4:30pm which will allow a gap in your availability each day.