According to Double AA's answer on a related question, "it can't hurt" to say an extra Shema' later if you missed the Zeman (set time) for it.
While it may be true to a certain extent that saying extra words of Torah are generally not harmful, what if the missed time was just prior to (or even on) Tish'ah BeAv? Would reciting an extra Shema' on Tish'ah BeAv pose a problem of learning Torah (which is prohibited, except for limited subjects, on that day)? Or is the fact that it is still part of the Tefillah, albeit a non-standard part, and only following an opinion rejected by most Posekim, enough to allow it to be recited?
