You can get good help on the Plots gitter: https://gitter.im/tbreloff/Plots.jl
In this case I cannot answer, as plot(0:.1:10,Any[ x->K*cos(x) for K in [-2,-1,1,2]]) leads to this plot for me:
I think your “real-time” plotting problem is a Jupyter problem, rather than a Plots problem. Try running your code in Atom or from the REPL to verify.