[BioC] Doubt on time course design

[Stefano Capomaccio [guest]]

I'm writing because I have a doubt on how to perform a DGE analysis with edgeR.
I followed both the tutorial and some interenet posts, but I got confused and I'm not sure on how to properly account for variation between individuals in my experimental design that is the following:

RNA-Seq data of 6 subjects at 4 different time points (24 obs). There is no control/treatment.
My goal is to reveal genes that are differentially expressed between the time points.

Should I design the matrix as follows?

designMatrix <- model.matrix(~subjects+timepoints)

Or there is something that I misinterpret?
Any advices on this issue?

Thank you all for your cooperation.

 -- output of sessionInfo(): 

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