I had pages added to my passport book 2 weeks ago at the Embassy in BsA.
It was rather painless. Fill out and print your form before you go.
As Gaucho mentions, you can click the 52 pages for the same price to get more pages.
You can skip the line, VIP style, and go right to the window.
Arrive between 8:30 and 10:30 I believe.
Once inside, I had to take a number, wait 5 minutes, then pay, wait 2 minutes and leave.
Need to return between 3 and 4 the same afternoon and its ready to go.
Hardest part was finding parking, take a taxi.