Prague Castle - time to tour the site?

with the B tour you are going to need a full morning, but remember any ticket you buy is valid for 2 days.as you enter each area you ticket will be scanned and once in that area you cannot return with that ticket.
there are lots of the castle you can see free just area like the interior of the buildings and Golden lane you must have a ticket to access.I often just have a wander through the castle area and you can get into St Vitus without a ticket but only into the front area of the building.
There is also security lines to get through and they can vary from a minute to 30 minutes or more especially if coming in by the Prazsky hrad entrance.
https://www.hrad.cz/en/prague-castle-for-visitors/castle-map.

The entry time does vary a lot. My first time through, I used the usually-busier entrance, but it was in the afternoon and the security lines were short. The second time I approached from the north and the lines were long, made worse when I randomly chose the line on the right side of the street without realizing that there was only one person working on that side and he was using a hand-held wand, vs. two people with metal-detector gates on the other. My guy was also extremely conscientious. I'd still be in that line if a second security guy hadn't shown up.

I only went in St. Vitus, the St. Vitus Treasury (separate and expensive ticket), and Golden Lane, so I don't have a useful time estimate for you.

Might seem a bit strange but I'd say start with 60 minutes then if you are Catholic, add 60 minutes. If you're a Gothic architecture fan add 30 minutes. If you're a photographer add 60 minutes. If you like gardens and scenic views add 30 minutes. If you like art add 60 minutes. If you include the Great South Tower (Not on Circuit B - separate ticket CZK150) add 30 minutes. So really I guess you are looking at 2-3 hours but spent in different places depending on your interests.

I spent about 3 hours total touring the Castle and St Vitus, and the part I loved the most was the Golden Lane, such charming little houses and Kafka lived in one of them with his sister at one point in his life.

Does anyone have a recommendation as to choosing Tour A vs. Tour B - or just wandering through the free parts?

Circuit A really Circuit B plus the "Story of Prague Castle" exhibition and the Rosenberg palace. As the previous poster said, people really buy the circuit tickets to see Golden Lane so gen up on that to see if you think you'd like it or not. Otherwise, if you're not too struck on Gothic architecture or the lane then skip the circuit tickets, buy tickets to individual exhibitions, enjoy the South Garden, take a look in ST Vitus (just to the entry part). Then if you like art then the Prague Picture Gallery is CZK100 and the great South Tower CZK150. Lots of options.