It all depends on the geometry and the types of stars.
Castor is a 7 star system. It has 3 sets of stars. Castor A and B both have a star somewhat larger and brighter then our sun and dwarf companion. Caster C has only dwarf stars.
Castor Aa and Ab are separated by about 0.022 AU, Castor Ba and Bb are separated by about 0.03 AU. Since both A and B are brighter than our sun (36 times for A, 14 times for B), the habitable zone would be around 6(A) or 4(B) times further away than our system. I.e., a habitable planet would orbit so far away from the Aa Ab pair, that the orbit would be stable. At worst, every few days, the occlusion of the primary by its dwarf companion would result in a dimming as the bright star was obscured.
C is so far away (1100 AU) and dim, that it would nothing more than a star in the night, albeit planet like in that it orbits in about 14,000 years.
A & B have orbit each other in 467 years at a distance of about 110 AU. This means that if you are at B looking A, A would be about 323 times dimmer than our sun from the earth which is also about 1200 times brighter than our moon. So, when you planet is between A and B, the nighttime sun would still be quite bright.
If you construct a rosette of 6 equal suns, you can theoretically orbit at an appropriate rosette in an entirely stable manner with normal day and night cycles. Since each sun would fall in Lagrange points, the rosette should be stable over long time periods even with minor perturbations coming from planets or other stars 110 AU away. With a large central black hole, the rosette is even more stable, though orbital speeds of everything else is necessarily considerably faster.