Conditions of the first (blue markers) and second (orange markers) observed transits showing the airmass (top panel), seeing (middle panel), and the S/N (bottom panel) for each exposure. The S/N was calculated from the Na I D doublet orders. The dashed black lines show the beginning and end of transit. The dashed red line marks the S/N =15 threshold, below which exposures were discarded. The circular markers correspond to 300 s exposures, and the lighter shaded triangular markers are used for 500 s exposures.