Advanced era in PBR is essentially the LATE General War years, when X-ships first came on line (when it was just Modified CA's with X tech added) and extends (theoretically) far enough into the future to include the fielding of CLX's, DDX'X and FFX's and the first X-squadrons, which I believe occured right about the end of the war and continued to develop prior to the Andromodan Invasion.
Both options are very simple.
Option A: you can have a single X-Heavy Cruiser (which counts as a Command Variant and is listed as such) and the 2 other ships can be non-Xships. Those other 2 ships most also conform to normal PBR rules concerning Support Ships, ect.
This option emulates the typical use of the early X-cruisers as well as the one philosophy of the use of X-tech, which was to use X-CA's in place of DN's in otherwise normal tech squadrons/fleets
Option B: every ship in the force has to be and x ship, but it can be any combination with normal PBR rules applying. This would allow a single X-CA (which automatically fills the Command slot) and 2 smaller x hulls or it could be all x hulls, allowing an FFX or DDX squadron.
This option simulates the OTHER philosophy and the later development of x-tech deployment, which was for squadrons or small fleets made up solely of X ships, in order to allow their greater mobility and full potential of their tech to be brought to bear.
Again, late era: can't use the Late era X ships.
Adavanced era: can use the late era x ships, can't use the Advanced era ships.
Option B: