Dubnium-268 has a half life of 29h and 270, 23.15h. I know of the island of stability but if dubnium is in it, the island is very small as only rutherfordium has isotopes that approach the same stability. Is there some special property of the two nuclides that stabilise them?
Explaining the nuclear structure (...and therefore any other properties like half-life or even mass) is still an open topic of research. The models at disposal (see for example Two-Center Shell Model) which are used for super heavy nuclei searches are generally non ab-initio, therefore no fundamental conclusions can be drawn regarding the underlying physics. In fact the closest we have got with current models in predicting super heavy nuclei half-lives is up to same order of magnitude (search for articles by W. Greiner, V.Zagrebaev. search for Viola-Seaborg formula). Although I am sure that some model-related explanation can be found to account for this in a model that manages to reproduce it. But indeed, currently the location of the island of stability is believed to be found around Z=120, so these nuclei are most likely to part of the many deviations from typical behaviour that we find in the Segre's Chart of Nuclei. You can have a look here (Structure of super heavy nuclei) for some further info on our knowledge of super heavies.