In general the error you are getting is telling you that if you want to plot one variable against another they both have to have the same number of elements, and yours do not have the same number of elements
Please supply your actual code where you define x1, x2, Data and timeline and we might be able to get a better idea of where things are going wrong.
Regarding your question about having the time display in minutes. When plotting with time as the x axis you can define the "x" variable as a MATLAB datetime array and it handles the scaling and so on nicely.
By the way, I notice in your code that you have Data as the first argument to plot and timeline as the second argument. This will put timeline as the vertical axis in your plot. Is this what you want?