I’d like to know if it is mutar to have marital relations before shahrit. If it is not, since what hour? Thanks
There is no prohibition against relations before Shachrit. In general, from the time of Alos Hashachar one should ideally not engage in any activity that takes considerable time and should be focused on preparing to daven. However, when one has a set time to daven and there is a need to do something important and particularly a mitzvah, this would be permitted before Shachris, provided he will daven by the proper time.
See Shulchan Aruch O:C 89:2,3. See Mishna Brura ibid. s”k 36 regarding a mitzvah.
Aishel Avraham Mebutchath ibid. is lenient when something will be unavailable or impossible after davening based on the principle of davar haved. See Halichos Shlomo Tefilla 2:5.