Phase coverage for SAINT-EX and Artemis data. Top: evolution of the phase coverage of a hypothetical planet orbiting TOI-2257 as a function of the period, derived from SAINT-EX and Artemis observations (blue dots). The effective phase coverage is the integral of the phase coverage over the 0.1–15 day period range and is equal to 59%. The dotted red (purple) line indicates the period above which the phase coverage is always inferior to 80% (40%), which corresponds to the period of 3.78 days (8.71 days). We note that periods equal to an integer number of days are significantly less covered due to day-night cycles in ground-based observations. Bottom: graphical visualization of the coverage of TOI-2257 with SNO and SAINT-EX for a hypothetical planet with orbital periods of 3.78 and 8.71 days, respectively. Each blue circular arc represents one night of observation; its size is proportional to the number of hours observed each night, and a full circle depicts a duration of 3.78 (8.71) days.