  The time which a diffusing particle spends in a certain region of space is
known as the occupation time, or the residence time. Recently the joint
occupation time statistics of an ensemble of non-interacting particles was
addressed using the single-particle statistics. Here we employ the Macroscopic
Fluctuation Theory (MFT) to study the occupation time statistics of many
\emph{interacting} particles. We find that interactions can significantly
change the statistics and, in some models, even cause a singularity of the
large-deviation function describing these statistics. This singularity can be
interpreted as a dynamical phase transition. We also point out to a close
relation between the MFT description of the occupation-time statistics of
non-interacting particles and the level 2 large deviation formalism which
describes the occupation-time statistics of a single particle.
