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We present a study of timing properties of the accreting pulsar 2S 1417-624observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMTand NICER observations. We report a dramatic change of the pulse profiles withluminosity. The morphology of the profile in the range 0.2-10.0keV switchesfrom double to triple peaks at $\sim2.5$ $\rm \times 10^{37}{\it D}_{10}^2\erg\ s^{-1}$ and from triple to quadruple peaks at $\sim7$ $\rm \times10^{37}{\it D}_{10}^2\ erg\ s^{-1}$. The profile at high energies (25-100keV)shows significant evolutions as well. We explain this phenomenon according toexisting theoretical models. We argue that the first change is related to thetransition from the sub to the super-critical accretion regime, while thesecond to the transition of the accretion disc from the gas-dominated to theradiation pressure-dominated state. Considering the spin-up as well due to theaccretion torque, this interpretation allows to estimate the magnetic fieldself-consistently at $\sim7\times 10^{12}$G.

Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT