  In the propagating oscillatory shock model, the oscillation of the post-shock
region, i.e., the Compton cloud, causes the observed low-frequency
quasi-periodic oscillations (QPOs). The evolution of QPO frequency is explained
by the systematic variation of the Compton cloud size, i.e., the steady radial
movement of the shock front, which is triggered by the cooling of the
post-shock region. Thus, analysis of energy-dependent temporal properties in
different variability time scales can diagnose the dynamics and geometry of
accretion flows around black holes. We study these properties for the high
inclination black hole source XTE J1550-564 during its 1998 outburst and the
low-inclination black hole source GX 339-4 during its 2006-07 outburst using
RXTE/PCA data, and we find that they can satisfactorily explain the time lags
associated with the QPOs from these systems. We find a smooth decrease of the
time lag as a function of time in the rising phase of both sources. In the
declining phase the time lag increases with time. We find a systematic
evolution of QPO frequency and hard lags in these outbursts. In XTE J1550-564,
the lag changes from hard to soft (i.e., from a positive to a negative value)
at a crossing frequency ($\nu_C$) of $\sim 3.4$ Hz. We present possible
mechanisms to explain the lag behavior of high and low-inclination sources
within the framework of a single two-component advective flow model (TCAF).
