Calling both prayer and fasting “time-bound acts” does not make their time function identical. Prayer time is analyzed as a container (ẓarf), while the appointed day of Ramadan fasting is treated as a measure (miʿyār). Different consequences follow for identification and intention.
The possibility of different prayers in a prayer window is not identical to the legal treatment of fasting on a prescribed Ramadan day. Yet having an intention at all must remain distinct from specifying the particular fast within that intention.
Error: Inferring identical intention rules merely from the fact that both acts involve time. Correction: Analyze the function of the time, the act, and any relevant juristic exceptions separately.