There is an obligation to set "times for learning torah." How exactly does one fulfill this obligation? Do you have to designate specific times in the day e.g. 9-9:30 am, or can it be a specific amount of time of learning each day at any time? And does it have to be time specifically? (As opposed to pages, etc.) sources, please.
The obligation to set aside time daily to learn Torah is discussed in Shulchan Aruch OC Siman 155 and Siman 238. The wording of Shulchan Aruch ("He should establish a time to learn. This time should be set, and he should not skip it, even if he things he will make allot of profit") seems to imply it should be a specific time in the day. The Seder Hayom (a contemporary of the Beis Yosef) and Kaf HaChaim (Ois 13) both emphasize it should be a set time in the day.
The question whether it should be a set amount of time or a set amount of material is discussed in the Sefer "Betoraso Yehege" (pg. 339 footnote 11). From the above sources it would seem it should be a an amount of time, however the Mishna Berura in OC 238:2 seems to imply it could be an amount of pages. He writes that R' Chaim Kanievesky wrote to him that either is acceptable.