Two updates for you all:

1. Karawang Station is now open! Journey time from Halim is less than 10 minutes. Not all Whoosh trains stop there, so be sure to check. Note that if the Whoosh stops here, it adds a few minutes to the total journey time Halim - Bandung.
2. In-app refunds and rescheduling have been greatly improved. You can now book a ticket and change the time of departure very easily with a few clicks (you used to have to refund and rebook (losing 25% of ticket cost).