Subject: Universe inflation : what about the time flow ?

A recent study about SN seemed to show that universe expansion speed is increasing.
Now scientists seek for another models (antigravity, hidden energy...) to explain that phenomenom.
I wonder why in all these theories we assume that the "time flow" is constant. I mean relative time depends on gravity and maybe other things. How can we say that the time flow is the same than billions years ago ? Many things have evolved since these times, for instance the global entropy.
Maybe the universe expansion speed is constant and time flow is lowering (since v=dl/dt, the measure of dt is lower for the same displacement) ???

Re: Universe inflation : what about the time flow ?