(Bamidbar 28:3) "And you shall say to them": This is an exhortation to beth-din (to charge the people). "This is the fire-offering which you shall offer up to the L-rd … two for the day." Shimon b. Azzai says: "two for the day" — opposite the "day" (i.e., opposite the sun). You say this, but perhaps the meaning is: "two for the day" — an obligation (to be slaughtered) on that day? (Ibid. 4) "The one lamb shall you offer in the morning, and the other lamb shall you offer towards evening" already speaks of the obligation for the day.
How, then, are we to understand (here) "two for the day"? As opposite the day (i.e., the sun) — whence they ruled: The morning tamid was slaughtered at the north-west corner (of the altar) at the second (slaughtering) ring, and the evening tamid at the north-east corner at the second ring.