Checked while we were out today and the office at the Kuta Paradiso in Jl. Kartika Plaza is still open for pre book ins.
8am to 4pm Monday to Friday
9am to 3pm Saturday, Sunday and holidays
Not sure where the poster, from a couple of days ago, got the info you could only do it at the airport now, but it was incorrect.
Don't forget to take your passports and tickets. They will only do it no earlier the the day before the flight