Purity: Wudu When Time is Short
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 279:
If there is so little time [before the end of the prescribed time for prayers] that by performing wuḍūʾ the entire prayer or part of it would have to be performed after its time, then one must perform tayammum. However, if the time required for performing tayammum and wuḍūʾ is the same, then one must perform wuḍūʾ.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)