  Highly entangled biphoton states, generated by spontaneous parametric
processes, find wide applications in many experimental realizations. There is
an increasing demand for accurate prediction of their time-dependent detection.
Unlike approaches that have emerged so far, this paper presents an approach
providing full time-dependent counting statistics in terms of efficiently
computable formulas, valid for a wide range of entanglement and arbitrary
interaction times. General spatial modes are taken into account to describe
free space and fiber propagation. The time intervals that correspond to the
statistics are classified according to their widths. Apart from large and small
widths compared to the temporal correlation width, intermediate interval widths
give access to accidental correlations between separated time intervals.
Moreover, the approach is easily applicable to a modular array of arbitrary
optical components and external influences. This is demonstrated on phase-time
coding, where the detuning of the interferometers affecting Franson
interference is investigated. An acceptable range for the detuning is
estimated, such that the security of the key is not compromised.
