Wings air are now flying daily from Kupang to Rote, departing from Kupang at 3pm which allows you to connect with the Garuda 11am flight from Bali to Kupang.
The flight departs Rote at 4pm to Kupang, unfortunately this doesn’t connect with Garuda flight back to Bali, so an overnight stay is required.
If you wish to connect with the 4pm Garuda flights you need to take the fast ferry from Rote to Kupang.