Expected number of detections by CTA-MST using the one-shot observation strategy (left column). The estimates of the number of possible VHE counterparts are based on the on-axis BNS systems (systems injected with θ_v < 10° in our simulations) and are evaluated as described in the text (see Eq. (6)). These estimates assume that all BNS produce a jet. They take into account the sky-localization (Ω_i) of each event, the MST field of view of 30 deg², the CTA duty cycle of 15%, and the CTA visibility limited to a zenith angle larger than 60° (minimum elevation of 30°). The fraction of CTA time spent following all the GW alerts with the sky-localization smaller than the one indicated on the x-axis is given by the plots in the central column. To observe each event (independent of the sky-localization) the observational time (t_obs) is considered, given by the sum of slewing time (t_slew = 90 s), an additional re-positioning time (t_rep = 10 s), and the exposure time (t_exp = 20 s). The plots in the right column show the CTA time when only triggers with an observed θ_v < 45° are followed up resulting in a significant reduction of CTA time.