Fraction of OC members with assigned variability classes in GDR3 against log t, both in total numbers and for the four most populous variable classes individually. Only stars with M_G, 0 < 7 mag residing in OCs with extinction-corrected distance modulus μ + A_G < 9 are shown so that all member stars have m_G < 16. These simple cuts aim to improve the similarity of variability detectability with log t compared to not applying cuts, cf. Sect. D.