Molecular gas depletion time (t_dep = M_H2/SFR) as a function of redshift for our H I–selected sample (blue circles for high molecular gas systems and light-blue for low molecular gas mass systems), compares with literature scaling relations and emission-selected samples (Saintonge et al. 2017; Tacconi et al. 2018). The result from the stacked spectrum described in Sect. 3.2 is shown by the blue star. The solid red curve shows the empirically derived t_dep evolution for main-sequence galaxies from Tacconi et al. (2018), the dotted line marks the Hubble time at each redshift, the thin solid line represents the stellar mass doubling time (t_* = M_★/SFR) from Tacconi et al. (2020), and the dashed purple line is from the cosmic depletion timescales derived from the ALMACAL survey (Bollo et al. 2025). H I–selected galaxies, both from our sample and from high-redshift literature sources (grey dots; Klitsch et al. 2021; Neeleman et al. 2018, 2020, 2025; Fynbo et al. 2018; Kanekar et al. 2020, 2018; Kaur et al. 2022, 2025), consistently lie above the main-sequence relation, which indicates lower star formation efficiencies. Several galaxies exhibit t_dep approaching or exceeding the Hubble time, which suggests inefficient molecular gas consumption or suppressed star formation.