  Using the disc instability model and a simple but physically reasonable model
for the X-ray, extreme UV, UV and optical emission of dwarf novae we
investigate the time lags observed between the rise to outburst at different
wavelengths. We find that for ``normal'', i.e. fast-rise outbursts, there is
good agreement between the model and observations provided that the disc is
truncated at a few white dwarf radii in quiescence, and that the viscosity
parameter alpha is ~0.02 in quiescence and ~0.1 in outburst. In particular, the
increased X-ray flux between the optical and EUV rise and at the end of an
outburst, is a natural outcome of the model. We cannot explain, however, the
EUV delay observed in anomalous outbursts because the disc instability model in
its standard alpha-prescription form is unable to produce such outbursts. We
also find that the UV delay is, contrary to common belief, slightly longer for
inside-out than for outside-in outbursts, and that it is not a good indicator
of the outburst type.
