I don't know for metastable glass but you can read about the third law of thermodynamics which address the question of entropy and low temperature: https://en.wikipedia.org/wiki/Third_law_of_thermodynamics

Especially this might interest you:

"A classical formulation by Nernst (actually a consequence of the Third Law) is:

It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations."