IREX, Bob Tait's book and MDA
Don't forget that is only for day time that you can descend and make a visual approach before the circling area. Following the published approach you can descent to MDA, so If you break free from cloud ABOVE the MDA you may continue visually.
Joining a "normal" circuit is only done when VMC exists.
During night time, if you are clear of cloud, you must still continue to the circling area above the circling minima.
Hope this helps.