While the best practice is to use Next Available and let the system locate an appropriate time slot, an experienced scheduler who is familiar with the scheduling rules can select desired time slots directly. Simply click to highlight the time slot directly on the Scheduling calendar and then click New on the toolbar (or just double-click on the time slot). This will open an Appointment form that is pre-populated with the date, time, and site. You can then fill in the rest of the information and save.
The disadvantage to scheduling an Appointment this way rather than using Next Available is that there is no assurance that the Scheduling Block rules are being followed, although you will receive a warning if your proposed appointment breaks any of the rules established for that scheduling block (see example below—different violations will produce different warnings). Note that the warning does not stop you from scheduling the Appointment; it simply informs you of the conflict and allows you to decide whether to save it anyway.