We have investigated anomalously slow magnetic domain growth in an antiferromagnetic (AF) phase of isosceles triangular lattice Ising antiferromagnets CO1-xMgxNb2O6 with x = 0 and 0.004, by means of time-resolved neutron diffraction measurements. Applying the multi-profile-deconvolution analysis to the observed diffraction profiles, we have revealed that time evolutions of spin correlation lengths along the a and b axes, ξaand ξb, are well described by a power-law scaling form of ξ0α + La(t/τ α)n ( α= a,b) with a universal growth exponent of n = 0.2. The characteristic time scale of the domain growth, τα, was found to exhibit Arrhenius-type temperature dependence in the AF phase. A comparison between the results of the x = 0 and 0.004 samples has revealed that the nonmagnetic substitution significantly reduces the initial correlation length, ξ0a, and the activation energy in the Arrhenius-type temperature dependence of τα. We have alsofound that magnetic domain growth in a magnetic-field-induced ferrimagnetic phase alsofollows the power law with the growth exponent of n = 0.2. On the basis of these results, we have concluded that the existence of ferromagnetic Ising spin chains running along the c axis and the geometrical spin frustration in the ab plane are the keys to the domain growth kinetics in this system. The former and the latter govern the characteristic time scale and the growth exponent, respectively. [ABSTRACT FROM AUTHOR]