This paper deals with timing recovery for Impulse Radio (IR) ultra-wideband (UWB) communication systems, which is known to be a challenging task to accomplish. We focus on blind estimation approaches, with the aim of being able to operate with minimal constraints on the signal format (no use of pilot symbols). We consider also the blind timing estimation problem in the sense that no prior knowledge is needed on the modulation parameters. The proposed methods may contribute to develop flexible receivers, capable of synchronizing various IR-UWB signal formats from short data records, even if some key parameters are changed over time.