We report the discovery of HAT-P-24b, a transiting extrasolar planet orbiting the moderately bright V=11.818 F8 dwarf star GSC 0774-01441, with a period P=3.3552464+/-0.0000071 days, transit epoch T_c_=2455216.97669+/-0.00024(BJD), and transit duration 3.653+/-0.025hr. The host star has a mass of 1.191+/-0.042M_{sun}, radius of 1.317+/-0.068R{sun}, effective temperature 6373+/-80K, and a low metallicity of [Fe/H]=-0.16+/-0.08. The planetary companion has a mass of 0.681+/-0.031M_J and radius of 1.243+/-0.072R_J_ yielding a mean density of 0.439+/-0.069g/cm^3^. By repeating our global fits with different parameter sets, we have performed a critical investigation of the fitting techniques used for previous Hungarian-made Automated Telescope planetary discoveries. We find that the system properties are robust against the choice of priors.