«ثُمَّ هَذِهِ الْكَلِمَةُ تُسْتَعْمَلُ فِي الزَّمَانِ وَالْمَكَانِ وَالْفِعْلِ»
Fi can be used with time, place and an act. Each construction requires its own interpretation.
Time: “fi ghad” places something within tomorrow.
Place: “fi al-masjid” places an occurrence in the mosque.
Act: “fi dukhulika al-dar” relates a ruling to entering a house.
With time the question may be whether the first instant or an unspecified portion is meant. With place it may be the location of the affected person rather than the actor. With an act, fi can function conditionally.