The timescales you mentioned are related to different physical processes and phenomena occurring in different contexts. Let's break them down:
Transparency of the Universe: The statement that the entire Universe became transparent after 375,000 years refers to the epoch known as recombination. During this period, about 375,000 years after the Big Bang, the Universe cooled down sufficiently for electrons and protons to combine and form neutral hydrogen atoms. This allowed photons (light) to travel freely through space, making the Universe transparent.
Escaping a Yellow Dwarf: When you mention it takes 170,000 years to escape a yellow dwarf, I assume you are referring to the time it takes for photons generated at the core of a yellow dwarf star (such as our Sun) to reach the surface and be emitted into space. This timescale is associated with the energy transport mechanism within a star. Photons are generated through nuclear fusion reactions in the stellar core and then undergo a series of scattering and absorption processes as they make their way to the surface. Due to these interactions, it takes a considerable amount of time for photons to diffuse through the dense layers of a star, eventually reaching the photosphere and being emitted as light.
It's important to note that the physical processes involved in the transparency of the Universe and the energy transport within a star are fundamentally different. The Universe's transparency is related to the overall expansion and cooling of the cosmos, while the time it takes for photons to escape a star is influenced by complex interactions occurring in the stellar interior. These processes operate on different scales and involve different physical mechanisms, which is why the timescales associated with them can vary significantly.