How do you offer half-hourly options?

I'm offering one-hour appointments. When you select the day, you see:
8:00am
9:00am
10:00am
etc...

Is there a way to show half hours?
8:00am
8:30am
9:00am
9:30am
etc...

Also, I've got a minor quirk where the times appear (unclickable) before you select your day. Shouldn't they be hidden until you select the day?

Thanks