  In this paper, we study two large data sets containing the information of two
different human behaviors: blog-posting and wiki-revising. In both cases, the
interevent time distributions decay as power-laws at both individual and
population level. As different from previous studies, we put emphasis on time
scales and obtain heterogeneous decay exponents in intra- and inter-day range
for the same dataset. Moreover, we observe opposite trend of exponents in
relation to individual $Activity$. Further investigations show that the
presence of intra-day activities mask the correlation between consecutive
inter-day activities and lead to an underestimate of $Memory$, which explain
the contradicting results in recent empirical studies. Removal of data in
intra-day range reveals the high values of $Memory$ and lead us to convergent
results between wiki-revising and blog-posting.
