I've created single appointment times by setting recurring personal events on the calendar, preventing people from signing up for any times other than those I want displayed.
For example, let's say your service's duration is one hour, and you want to create openings for 10am and 2pm.
First set your business hours to the widest you would ever be working that day (e.g. 9am to 6pm, given the times you mentioned in your post). Then add personal events to fill in non-working times. In this case, you'd need three: 9am-10am, 11am-2pm, 3pm-6pm. Anyone going to your booking webpage would then only see two options to select from: "10:00am" and "2:00pm".
You can set personal events to repeat on certain schedules. For instance, if your 10am and 2pm availability is only true every-other week, you can set the personal events to repeat "every 2 weeks". You could then use a group of different personal events for another week to create different availabilities, setting them to repeat as well.
The more varied your schedule, the more repeating personal events you'll need to create to narrow down the available openings. But once they're set it should run smoothly.
If the weekly schedule isn't quite regular (for instance, you take a week vacation), you can quickly edit the personal events to move them forward or backward on the calendar.
If your schedule is extremely variable, rarely repeating, I'm afraid this method might take a lot of work. But it's the only way I know to create specific appointment time openings.
