This has to do with the mass/energy of the Higgs boson.
Here is the relevant quote from the Wiki article on the Higgs boson...
"In the Standard Model, there exists the possibility that the underlying state of our universe – known as the "vacuum" – is long-lived, but not completely stable. In this scenario, the universe as we know it could effectively be destroyed by collapsing into a more stable vacuum state.[33][34][35][36][37] This was sometimes misreported as the Higgs boson "ending" the universe.[h] If the masses of the Higgs boson and top quark are known more precisely, and the Standard Model provides an accurate description of particle physics up to extreme energies of the Planck scale, then it is possible to calculate whether the vacuum is stable or merely long-lived.[40][41][42] A 125 – 127 GeV Higgs mass seems to be extremely close to the boundary for stability, but a definitive answer requires much more precise measurements of the pole mass of the top quark.[32] New physics can change this picture.[43] "
From
https://en.wikipedia.org/wiki/Higgs_boson
And this has nothing to do with the temperature of any voids.
Also, not being an expert on Differential Geometry, Gauge theory and Topology, I am not so sure a symmetry break travels at the speed of light, as I'm not sure there is information transport.
The example which brings this to mind is A Guth's from his original Inflationary theory.
Consider a symmetric dinner table arrangement where a fork and knife are placed between each plate.
It is certainly symmetric.
But as soon as one guest 'breaks' the symmetry by choosing either the fork/knife on his left, or his right, the choice has been immediately made for every other guest at the table.
Maybe someone more familiar with this issue can explain.