Suppose the evolution of the stock price is given by Geometric Brownian Motion. Futher I assume that the risk free rate process is given by CIR model. In both models there is a time increment dt. To my understanding dt is dependent on day count convention. There are 252 bussiness days in one year. For rates one should take into account their day count conventions e.g. Act/Act, Actual/360 and so on.
How do people deal with this issues in real world applications?
Thanks in advance.