-click in the Time Slider and select Keys > Add Inbetween from the menu that appears to insert an Inbetween at the current time.
-click in the Time Slider and select Keys > Remove Inbetween from the menu that appears to delete the Inbetween at the current time.
When using Remove Inbetween, the space between keys is decreased. This may cause keys to conflict and act unpredictably.