In the advent of astronomical facilities to observe multiple sources in a single observation it is necessary to automate innovative strategies that select targets in an optimal way to make the most of telescope time, the tip-end of new scientific discoveries on astronomy. Meeting this need, we developed an exposure time calculator (ETC) Extension for Multi-Object Observation (EMOO) to be used with MANIFEST, a fiber positioning facility for the GMT. The code is currently built upon the ETC of the GMT-Consortium Large Earth Finder (G-CLEF), a first-light instrument for the GMT, which is serving as a base test model for the results presented in this work. This new capability must be able to deliver the maximum signal to noise ratio (SNR) for each target, balanced within a range provided by the user, with no saturation and in a limited amount of time. That means an optimal exposure time must be partitioned between a minimal number of observations blocks, always letting enough time to fulfill the requirements in all blocks. In order to mitigate the impact of unnecessary simulations our algorithm is inspired by binary searching routines and the results, compared to the classical approach, show that we can deliver a more uniform and higher SNR distribution across an optimal set of observations. In other words, we increased the SNR by decreasing the observation time.