myfriend-
In Menachos 99b Ben Dama asks R’Yishmael: I, who learned the entire Torah, can I learn Greek wisdom? He answered that the Pasuk says, “The Torah should not depart from your mouth and learn it day and night” – if you find time which is not day or night only then can you learn Greek wisdom.
The pshtus is that the halacha is not in accordance with that gemara. The gemara over there brings a middle shita that says one is yotzei lo yamush with krias shma in the morning and evening, and this is the stama d’gemara in Nedarim, and is brought down l’halacha by the Shach in Hilchos Talmud Torah. Surely one who has time to learn and does not do so out of laziness falls under the category of moshav leitzim and is not doing what he was put here for, but l’halacha one is mekayeim the mitzva with a set time in the morning and evening.