Can you not do two plots with overlay? I.e. plot all values < 25jun and give those a style color, then plot all values > 25jun and give those a style color different to the first? That would be the quickest way I can think of. The other way would be to use groups. So in your data assign < 25jun as group1, > 25jun as group 2, then use the group= options in the plot. The best reference for graphing is here:
http://blogs.sas.com/content/graphicallyspeaking/
And please avoid coding all in uppercase, it really makes code hard to read.
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