1)    When the time for praying has been reached, it is forbidden for a person to start learning Torah. However, if his regular custom is to go to the synagogue to pray, or he asked his friend who is not learning at that time to remind him to pray, he is allowed to start learning. (Mishne Berurah 89)

2)    One who teaches Torah to others, is allowed to teach even after the time for praying has been reached, as the merit of a group of people is very great, and if they will not learn now, they will waste their time and not learn. If, however, he is worried that the time for saying Shema will pass, he must recite it beforehand. (ibid)