Quasi steady state assumptions are often used to simplify complex systems of
ordinary differential equations in modelling of biochemical processes. The
simplified system is designed to have the same qualitative properties as the
original system and to have a small number of variables. This enables to use
the stability and bifurcation analysis to reveal a deeper structure in the
dynamics of the original system. This contribution shows that introducing
delays to quasi steady state assumptions yields a simplified system that
accurately agrees with the original system not only qualitatively but also
quantitatively. We derive the proper size of the delays for a particular model
of circadian rhythms and present numerical results showing the accuracy of this
approach.Comment: Presented at Equadiff 2013 conference in Prague. Accepted for
publication in Mathematica Bohemic