During transit, stellar light gets filtered through the terminator region of an exoplanet, allowing us to peek into their atmospheric structure and composition. Because of their complex 3D nature, however, this region is most likely not homogeneous. Hot, highly irradiated and tidally-locked giant planets in particular have been predicted to have different properties in their morning (i.e., night-to-day) and evening (i.e., day-to-night) terminators, implying they might have distinct temperature, pressure and thus compositional profiles which would give rise to different spectra on each side of it. Constraining those might give precious insights into circulation patterns and compositional stratification which might prove to be fundamental  for our understanding of not only the weather patterns in the planets under study, but also of planetary formation signatures which might only be possible to extract once these features are well understood. In this talk, I will review the state-of-the art on the modelling predicting this effect and observational prospects on their detection, with a special focus on the role that high and low-resolution ground-based spectrographs could have on the quest to constrain the mornings and evenings on these distant worlds.