Diagnosability is the property of a system to have sufficient observable information to guarantee the diagnosis of a fault. Here, the considered fault is a timed fault, i.e. an unobservable event that occurs in bounded time since the start of the system. Starting with a system modeled as a Time Petri net that is not diagnosable, this work proposes a method that provides adjustments by restriction of static time intervals to ensure the system becomes ∆-diagnosable for that fault. These adjustments are characterized by a set of constraints over interval bounds and then provide a set of solutions, if any, to ensure the diagnosability of the system.