a second is defined as the time it takes for a caesium atom to oscillate exactly 9192631770 times, at least according to the SI. a meter is then defined, as you said, as the distance light travels in 1/299792458 seconds, which corresponds to some large number of oscillations of those caesium atoms. these numbers are pretty much arbitrary though, we just picked them to match our previous, less precise, definitions of meters and seconds. but using oscillations of caesium atoms and speeds of light in your is completely equivalent to using meters and seconds, except that the latter units are more familiar to us
a second is defined as the time it takes for a caesium atom to oscillate exactly 9192631770 times, at least according to the SI. a meter is then defined, as you said, as the distance light travels in 1/299792458 seconds, which corresponds to some large number of oscillations of those caesium atoms. these numbers are pretty much arbitrary though, we just picked them to match our previous, less precise, definitions of meters and seconds. but using oscillations of caesium atoms and speeds of light in your is completely equivalent to using meters and seconds, except that the latter units are more familiar to us