Shulchan Arukh, Orach Chayim Siman 157
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
דיני זמן קביעות לסעודה. ובו סעיף אחד
כשיגיע שעה רביעית יקבע סעודתו ואם הוא תלמיד חכם ועוסק בלימודו ימתין עד שעה ששית ולא יאחר יותר דהוי כזורק אבן לחמת אם לא טעם מידי בצפרא:
Laws of When To Establish One's Meal. Containing 1 Se'if
When the fourth hour [of the day] arrives, one should establish his meal. And if he is a Torah scholar and he is occupied with his learning, he should wait until the sixth hour, but he should not delay more than that for it is considered like throwing a stone into a [wine] pouch if he did not eat anything that morning.