Dating very old objects/events After reading this space timeline, I have wondered how they managed to make these assumptions about various events like when the first black holes formed. This is obviously far beyond the good ol' carbon-14 dating procedure.
One property of distant objects, that follows from the limited speed of light, is that we are observing them in the past; the light that they emit takes time to reach us. For very distant objects, we are effectively observing the universe at a very early time.

Objects that are very far away, such as distant galaxies, are receding away from us, which causes the light that they emit to be doppler shifted. The recession velocity is proportional to the distance away, and in turn so is the magnitude of the redshift. This redshift allows us to put a number to the distance away; combining this with the speed of light limit allows us to determine how old the light we are observing from them is.

These two effects, the limited speed of light and redshift, effectively allow us to determine an evolutionary timeline for the universe, and place constraints on when certain objects appear.