In Tristram Shandy, Tristram is in a race against time: although he's writing as fast as he can, he can't write fast enough to keep up with his life. But unlike life, which can only be lived in one direction, writing moves backwards and forwards in time and so it actually can create time where time didn't exist.
That's the thing about writing: it's never quite up-to-the-moment. There's always a lag between event and record, so it turns out that these two themes—writing and time—are interconnected. Writing allows Tristram to play with time; but time means that Tristram will always be enslaved to his writing.
The main antagonist in Tristram Shandy is time.
Tristram Shandy suggests that storytelling is a way of beating time at its own game.