From what I know it can take forever for a pearl to actually to form, if that's what you're asking. After all, they happen when a grain of sand or something else tiny gets in and the oyster protects itself from it by covering it in lots of materials. So it would take many years.
My tanks (so far
5.5 gallon Planted Dwarf Puffer tank (2 Dwarf Puffers and a lot of RCS!)
16 Gallon Planted
(GBR pair, 3 amano shrimp and a whole bunch of snails!)