The purpose of doing this, is if a candidate has spoken to you, say on the phone, and said a specific time they would like an interview. Then you can manually choose that time slot to send them, as opposed to the generic all availability slots which may get booked up by another candidate.
What you need to do
Go into the interviews screen for a job by clicking on the 'Interviews' tab on the green panel.
Make sure you've set up the configuration and set future availability! Then press the below:
The below pop-up will appear, where you choose the time you want to send the interview for, based on the availability options previously selected:
Click schedule the interview, and the candidate will receive the standard email invite, however now they will only see the time option you have chosen for them. They will then confirm this time and the invite will go into the hiring teams' calendars.