Cooking temparature Jeni Britton base mix
A small question on the cooking temperature of Jeni Britton's base mix:
At a certain point Jeni's white base mix is to be put on a rolling boil during four minutes on a medium heat.
Egg-based mixes are only to be heated to +-170/175°F.
She's mentions that timing is of the utmost importance.
Why is that so, from a chemical point of view? Why does this mix require longer and stronger heating?
Thanks for any comment,