  We present a detailed analysis of the length- and timescales needed to
approach the critical region of MBL from the delocalised phase, studying both
eigenstates and the time evolution of an initial state. For the eigenstates we
show that in the delocalised region there is a single length, which is a
function of disorder strength, controlling the finite-size flow. Small systems
look localised, and only for larger systems do resonances develop which restore
ergodicity in the form of the eigenstate thermalisation hypothesis. For the
transport properties, we study the time necessary to transport a single spin
across a domain wall, showing how this grows quickly with increasing disorder,
and compare it with the Heisenberg time. For a sufficiently large system the
Heisenberg time is always larger than the transport time, but for a smaller
system this is not necessarily the case. We conclude that the properties of the
MBL transition cannot be explored using the system sizes or times available to
current numerical and experimental studies.
