Ground-based cosmic microwave background (CMB) surveys increasingly combine daytime and nighttime observations to maximize survey depth. Time-variable solar illumination and atmospheric loading can imprint spatially and temporally varying systematics so that arbitrary data splits are not interchangeable at the map level. We study this using the Atacama Cosmology Telescope (ACT) Data Release 6.02 (DR6.02) daytime archive for the PA6 array, comparing Day-Side (DS) and Day-Night (DN) geographic labels with four-way temporal jackknives at 150 GHz for beam-corrected temperature autospectra and for temperature-only quadratic-estimator (QE) reconstructions of the lensing convergence kappa. In ten multipole bins from roughly ell = 557 to ell = 3625, the mean temperature power ratio C_ell^TT(DS)/C_ell^TT(DN) is about 0.31 with jackknife errors; lensing autospectrum ratios are closer to unity but show a large chi-squared against R=1 in every bin when neglecting bin–bin covariance. DS–DN temperature cross-spectra are consistent with null at below 0.1 sigma per bin, while DS–DN QE cross power lies far below autospectra, as expected for largely disjoint footprints and uncorrelated reconstruction noise. Binned QE amplitudes at 90 and 150 GHz on an all-array daytime coadd correlate at r = 0.998 (linear) and r = 0.996 in log10 amplitude. We interpret DS/DN contrasts in terms of footprint geometry, differential weighting and noise, and relative calibration, and relate these split-level diagnostics to ACT DR6 lensing pipelines and the recent ACT daytime lensing demonstration.