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There are many system of units used in physics. In the CGS, the units are,
length : centimetre
mass : gram
time : second
And in the MKS system the units are,
length : metre
mass : kilogram
time : second
Though other units change in different systems, but time's unit never changes. Why?
The problem of the CGS system was that the base units of CGS were not coherent with the practical electrical units ampere and volt. In CGS, the unit of energy is the erg (1 erg = 1 g cm2/s2), whereas the electrical units volt and ampere result in 1 joule = 1 V A s = 107 erg. The joule was introduced in 1889. Although the joule is called a derived unit in SI, historically MKS and SI are derived from the joule.
Giorgi noticed that a small change in the prefixes of the base units of CGS could achieve coherence with the joule. His new base units were decimal (sub)multiples of the old base units, and only one of the base units had a prefix, similar to CGS. So the unit of length lost its prefix, $cm \rightarrow m$, while either the unit of mass or the unit of time obtained a prefix.
Giorgi's solution was to change the unit of mass: $ {joule} = [M]\ m^2\ s^{-2} \rightarrow [M] = 1\ {kg}$
Trying to change the unit of time did not result in a decimal (sub)multiple of the second: $ {joule} = g\ m^2\ [t]^{-2} \rightarrow [t] = 10^{-1.5}\ second$
