«أَنْتِ طَالِقٌ غَدًا»
“You are divorced tomorrow.”
«أَنْتِ طَالِقٌ فِي غَدٍ»
“You are divorced at some point within tomorrow.”
The expressions seem similar, but explicitly adding fi creates a potential reference to a portion of the day. Abu Yusuf and Muhammad treat presence and omission alike, locating the effect at dawn.
Abu Hanifa allows the explicit particle to leave room for a particular part of the day to be intended. The legal discussion therefore turns on the difference between omitting and expressing the particle.