Today’s times in Halacha

Hello Rabbi, I had the opportunity to study a little the famous dispute between the Magen Avraham and the Gra regarding the times of the day, whether they are measured from the rising of dawn until the stars appear or from sunrise until sunset. I wanted to ask if you have a side on the matter after studying the subject scientifically and halachically – whose opinion is more plausible? I also saw that the Gra in Orach 15945 Mil (as I think), brings the opinion of the sages of the profession, the astronomers, and tries to prove from them against the opinion of the Terumat Hashanah that the day begins at the rising of dawn, because there are astronomical difficulties with this. Do today’s astronomers also believe this? I would like to hear the Rabbi’s opinion on the subject, because I have a problem with this, an hour of sleep in the morning regarding the matter of the QS?