I don't have a manual handy for the IS304, but I believe that the numbers 1,2,3,4 refer to the 4 zones. It is capable of multiple start times, if I remember, so that is the section of the instructions you need to focus on.
I will try to find the manual. I have installed numerous of this model. I did think it was replaced with later model, but maybe not.
Found the manual on line>>http://www.rainbird.com/pdf/diy/man_ISAseries.pdf
You can have up to 3 start times per day. Programming start on about page 14.