When do we have to study the Written Torah? The answer can be found in Deuteronomy 6:7 and Deuteronomy 11:19. Let's take a look:
YLT Dt 6:4 . 'Hear, O Israel, Jehovah our God is one Jehovah;
YLT Dt 6:5 and thou hast loved Jehovah thy God with all thy heart, and with all thy soul, and with all thy might,
YLT Dt 6:6 and these words which I am commanding thee to-day have been on thine heart,
YLT Dt 6:7 and thou hast repeated them to thy sons, and spoken of them in thy sitting in thine house, and in thy walking in the way, and in thy lying down, and in thy rising up,
YLT Dt 6:8 and hast bound them for a sign upon thy hand, and they have been for frontlets between thine eyes,
YLT Dt 6:9 and thou hast written them on door-posts of thy house, and on thy gates.
YLT Dt 11:18 . 'And ye have placed these my words on your heart, and on your soul, and have bound them for a sign on your hand, and they have been for frontlets between your eyes;
YLT Dt 11:19 and ye have taught them to your sons, by speaking of them in thy sitting in thy house, and in thy going in the way, and in thy lying down, and in thy rising up,
YLT Dt 11:20 and hast written them on the side-posts of thy house, and on thy gates,
YLT Dt 11:21 so that your days are multiplied, and the days of your sons, on the ground which Jehovah hath sworn to your fathers to give to them, as the days of the heavens on the earth.
YLT Dt 11:22 'For, if ye diligently keep all this command which I am commanding you--to do it, to love Jehovah your God, to walk in all His ways, and to cleave to Him,
YLT Dt 11:23 then hath Jehovah dispossessed all these nations from before you, and ye have possessed nations, greater and mightier than you;
YLT Dt 11:24 every place on which the sole of your foot treadeth is yours; from the wilderness, and Lebanon, from the river, the river Phrat, even unto the farther sea is your border;
YLT Dt 11:25 no man doth station himself in your presence; your dread and your fear doth Jehovah your God put on the face of all the land on which ye tread, as He hath spoken to you.
As you can see, the answer to the question of when to study Torah is this: "and ye have taught/repeated them to your sons, by speaking of them in thy sitting in thy house, and in thy going in the way, and in thy lying down, and in thy rising up". This means that we must live our whole life through the Written Torah so to speak. Written Torah is life and life is the Written Torah. So EVERYTHING a person may do each day must be done according to or at least not contrary to the Written Torah.
You can't say that I will study 2 hours each day, but then I will do other things. Torah commands to study itself ALL THE TIME, so you have to have a copy available to you at all times during your waking hours.
I hope, this is all clear from the verses and from the explanation above.