Bold Times are a MINDBODY Business Mode setting used to control what times clients can book appointments for. To learn more about utilizing this feature, please take a moment to view MINDBODY's guide: https://support.mindbodyonline.com/hc/en-us/articles/205735258-Restrict-client-booked-appointments-to-bold-times.
If you have this option enable in your MINDBODY Business Mode, please make sure to enable them in the MINDBODY Appointment Element settings.