  Time-dependent entanglement entropy (EE) is computed for a single interval in
two-dimensional conformal theories from a quenched initial state in the
presence of spatial boundaries. The EE is found to be periodic in time with
periodicity equal to the system size $L$. For large enough $L$, the EE shows a
rise to a thermal value (characterized by a temperature $1/\beta$ determined by
the initial state), followed by periodic returns to the original value. This
works irrespective of whether the conformal field theory (CFT) is rational or
irrational. For conformal field theories with a holographic dual, the large $c$
limit plays an essential role in ensuring that the EE computed from the CFT is
universal (independent of the details of the CFT and of boundary conditions)
and is exactly matched by the holographic EE. The dual geometry is computed and
it interpolates between a BTZ black hole at large $L$ and global AdS at large
$\beta$.
