-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.