  PSR J1717-4054 is one of the small class of pulsars which null on
intermediate (~hour) timescales. Such pulsars represent an important link
between classical nullers, whose emission vanishes for a few rotations, and the
intermittent pulsars which null for months and years. Using the Parkes radio
telescope and the Australia Telescope Compact Array, we have studied the
emission from PSR J1717-4054 over intervals from single pulses to years. We
have identified and characterised nulling at three discrete timescales: the
pulsar emits during "active states" separated by nulls lasting many thousands
of rotations, while active states themselves are interrupted by nulls with a
bimodal distribution of durations; one to two rotations, or tens of rotations.
We detect no subpulse structure or flux density variations during active
states, and we place stringent limits (<0.1% of the mean active flux density)
on pulsed emission during inactive states. Finally, our high-quality data have
also allowed us to measure for the first time many important properties of PSR
J1717-4054, including its position, spindown rate, spectrum, polarization
characteristics, and pulse broadening in the interstellar medium.
