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We study the evolution of the temporal properties of MAXI 1820+070 during the2018 outburst in its hard state from MJD 58190 to 58289 with Insight-HXMT in abroad energy band 1-150 keV. We find different behaviors of the hardness ratio,the fractional rms and time lag before and after MJD 58257, suggesting atransition occurred at around this point. The observed time lags between thesoft photons in the 1-5 keV band and the hard photons in higher energy bands,up to 150 keV, are frequency-dependent: the time lags in the low-frequencyrange, 2-10 mHz, are both soft and hard lags with a timescale of dozens ofseconds but without a clear trend along the outburst; the time lags in thehigh-frequency range, 1-10 Hz, are only hard lags with a timescale of tens ofmilliseconds; first increase until around MJD 58257 and decrease after thisdate. The high-frequency time lags are significantly correlated to the photonindex derived from the fit to the quasi-simultaneous NICER spectrum in the 1-10keV band. This result is qualitatively consistent with a model in which thehigh-frequency time lags are produced by Comptonization in a jet.

The evolution of the broadband temporal features observed in the black-hole transient MAXI J1820+070 with Insight-HXMT