  In this paper we shed light on late time (i.e. with peak time t_{pk} \gtrsim
1000 s) flaring activity. We address the morphology and energetic of flares in
the window \sim 10^3-10^6 s to put constraints on the temporal evolution of the
flare properties and to identify possible differences in the mechanism
producing the early and late time flaring emission, if any. This requires the
complete understanding of the observational biases affecting the detection of
X-ray flares superimposed on a fading continuum at t > 1000 s. We consider all
the Swift GRBs that exhibit late time flares. Our sample consists of 36 flares,
14 with redshift measurements. We inherit the strategy of data analysis from
Chincarini et al. (2010) in order to make a direct comparison with the early
time flare properties. The morphology of the flare light curve is the same for
both early time and late time flares, while they differ energetically. The
width of late time flares increases with time similarly to the early time
flares. Simulations confirmed that the increase of the width with time is not
due to the decaying statistics, at least up to 10^4 s. The energy output of
late time flares is one order of magnitude lower than the early time flare one,
being \sim 1% E_{prompt}. The evolution of the peak luminosity as well as the
distribution of the peak flux-to-continuum ratio for late time flares indicate
that the flaring emission is decoupled from the underlying continuum,
differently from early time flares/steep decay. A sizable fraction of late time
flares are compatible with afterglow variability. The internal shock origin
seems the most promising explanation for flares. However, some differences that
emerge between late and early time flares suggest that there could be no unique
explanation about the nature of late time flares.
