Input sequence ordering for LSTM network
In order to make this decision, you have to think about what you want the representation to be passed to the next layer (or network output) to represent. 

If you want the representation at (after) $t = 0$ to be passed, you should pass the arrays in the $X = [x_{-n} .. x_0]$ order. The LSTM cell will form a representation of the sequence, then, at $t = 0$. 

In the reverse case, the representation will indicate the state at (before) $t = -n$

That's not to say that this is always a simple question for LSTM design- frequently in some domains such as NLP (text modeling), a bidirectional LSTM is used. This, basically, means both representations are implemented and used.