From several years different hypotheses have been suggested to connect, at least at low-accretion regimes, the physical processes regulating the conversion of an accretion flow into radiative energy and jet properties
and the black hole activity, in some universal relations across all the decades of black hole masses. The proper understanding of blazar variability at the various electromagnetic spectral bands is one important mechanism for these scenarios. In particular a peculiar and controversial phenomenology is the periodicity, postulated for long-term radio or optical flux light curves of few AGNs. The well-known BL Lac object OJ 287 (PKS 0851+202, S3 0851+20) is a high-variable extragalactic source with hints for approximatively cyclical optical outbursts. Also for this reason OJ 287 represents a case of substantial intensive and extensive multifrequency data allowing, under the strong assumption of a binary supermassive black hole central engine, to clock some General Relativity model predictions and properties of this object.