How to assign different mixtures at different times.
 

I have a question and hopefully someone helps me. How can I divide a time step to some parts and assign different mixtures at each divided time?

For example, suppose the whole time is 10 seconds and from 0 to 5 seconds, only mixture 1 flows into the domain and from 5 to 10 seconds only mixture 2 flows into the domain.
I really appreciate if someone helps me.