Karl Marx is the great philosopher of Time and Freedom.
His mature work, Capital, is an analysis of how we spend our days. Where do the hours of your life go? Who makes this decision? Yourself? Your employer? The state? Impersonal economic necessity?
For Marx, free time is the condition for freedom. This is so in the most material and direct sense possible. In any circumstance in which someone other than you determines what you do with the hours of your life, your freedom is to that extent constrained. The central issue of class struggle is the determination of who gets how many hours. The human purpose of Socialism is to allow the majority of people to control this decision with less external interference.
My friend Ted adds:
I think Marx's view of non-alienated leisure time supplements and enriches the standard liberal
view of freedom found in Hobbes, Locke, and the dominant "American" political tradition.
The liberal approach conceives of freedom as the absence of external constraints.
It proposes, in other words, a purely spatial conception of freedom.
Socialist freedom, though, would include not only a spatial but also a temporal dimension.