question #1 Sahih Muslim 608a, Book 5, Hadith 208 : What is the significance of completing at least one rak’ah before specific times in the context of prayer validity?

The Messenger of Allah (ﷺ) said: He who finds one rak’ah at dawn before the rising of the sun, he in fact finds the dawn prayer. and he who finds one rak’ah of the afternoon prayer before sunset, he in fact finds the afternoon prayer.