When is one to study Chitas and Rambam on Tishe Beav?

Set lessons of Torah study which have been instituted by Tzaddkim to be learned each day, may be learned after midday, however, not beforehand.[1] Thus, Chitas may be studied after midday by Mincha time.[2] After reciting Ein Kelokeinu before Mincha, one recites the Shiurim of Chitas.[3] [The daily Tehillim is recited, followed by Kaddish Yasom. One does not recite the daily Rambam until Motzei Tisha B’AV.[4]]

[1] Piskeiy Teshuvos 554:4 based on Taz 554:3; Gesher Hachaim 21:5

Other Poskim: Some Poskim rule it is to be completed only the next day. [Shaar HaTziyon 554:11; Mishmeres Shalom 40; Kaf Hachaim 554:19]

[2] Hayom Yom 9^th of Av; Sefer Haminhagim p. 97 [English]; Igros Kodesh 13:331

The reason it is not delayed until Motzei Tishe Beav: Regarding the daily learning cycle of Chitas, the night follows the previous day as is the rule by Kodshim, and hence one who learns the cycle at night, is to learn that day’s cycle as opposed to the next day’s cycle. Nonetheless, the above is only Bedieved, however initially Chitas is to be learned specifically during daytime and one is not to delay learning it until night, which is a status of Tashlumin and Bedieved which is only to be done in a time of need.  [Igros Kodesh 13:331; Likkutei Sichos 9:254; Toras Menachem 5749 2:209; Implication of Sichos and letters ibid that only after the fact do we say to do it at night]

[3] Hayom Yom 9^th Av; Sefer Haminhagim p. 97 [English]

[4] Morah Shiur of Rambam [edited by Rebbe] writes to study Rambam on Motzei Tishe Beav; Hiskashrus; Hilchos Uminhagei Chabad [Ginzberg] p. 284 footnote 94; Likkut of Rabbanbei Chabad Israel

The reason: Although it is a set daily study, nonetheless seemingly the Rebbe initially established in for after Tisher Beav as a stringency against learning Torah on Tishe Beav. [Rav Ginzberg ibid]