It can happen within a very short time, not all cigars do it, and bloom must be watched carefully, to make sure it doesn't turn into mold. Bloom is a good thing, but usually doesn't happen when cigars are in conditions of humidity under 65%, as many of us keep our cigars in that range.
Cigars in humidity ranges over 65%, especially for those who prefer the 70% range, can and do indeed develop bloom, but that can advance to mold quickly, if not observed on a regular basis. If it starts to turn fuzzy, but remains white, it is early stage mold, and should be wiped off, and humidity levels lowered immediately. Early stage mold is no problem, and if caught, and humidity levels lowered accordingly, will not advance again, nor mess up any of your cigars.
Bloom is an interesting thing to observe, but should not be obsessed over, nor seen as something that can be achieved. If your cigars develop it, great, if not, no problem either.