On a slightly different note, would anyone know if someone realized later in the day (before shkia) that the tefilin he put on was pasul, when he puts on tefilin again a) how long he needs to leave them on minimally and b) what he should daven while wearing them, if he already davened mincha?
Would it make no difference whether the shel yad and shel rosh were both posul or it was only one of the two, and should he make a bracha again on both parts of the second pair of tefilin if only one was pasul?