جوازه قبل الوقت
Its permissibility before the prayer time.
In the Hanafi analysis, attaining ritual purification is not intrinsically dependent on the entry of a particular prayer time. Where the conditions for tayammum exist, it can be performed before the time and remain useful for the later prayer if not invalidated.
A theory tying tayammum to permission for one timed obligation may impose a different limit. The underlying legal characterization explains the practical divergence.