Today’s times in Halacha

Hello Rabbi,
I had the opportunity to study a little the famous dispute between Magen Avraham and the Gra regarding the times of day, whether they are measured from the time of dawn until the stars appear or from sunrise to sunset. I wanted to ask if you have a side on the matter after studying the subject from a scientific and halachic perspective – whose opinion is more plausible?
I also saw that the Gra in Orach 1599 (d. 5 Mil, as I believe), brings the opinion of the sages of the sciences, the astronomers, and tries to prove from them against the opinion of the Terumat Hashanah that the day begins at dawn, because there are astronomical difficulties regarding this. Do the astronomers of our day also believe this?
I would love to hear the Rabbi’s opinion on the matter, as I have a problem with sleeping in the morning for the sake of the Kash 🙂