Time Petri nets (TPNs) are a classical extension of Petri nets with timing constraints attached to transitions , for which most verification problems are undecidable. We consider TPNs under a strong semantics with multiple enablings of transitions. We focus on a structural subclass of unbounded TPNs, where the underlying untimed net is free choice, and show that it enjoys nice properties in the timed setting under a multi-server semantics. In particular, we show that the questions of firability (whether a chosen transition can fire), and termination (whether the net has a non-terminating run) are decidable for this class. Next, we consider the problem of robustness under guard enlargement and guard shrinking, i.e., whether a given property is preserved even if the system is implemented on an architecture with imprecise time measurement. For unbounded free choice TPNs with a multi-server semantics, we show decidability of robustness of firability and of termination under both guard enlargement and shrinking.