It's widely accepted among players that the optimal times to play slots are early morning or evening, with peak hours typically occurring between 8 pm and 2 am. Take some time to watch the particular machine to gauge when it is most likely to pay out.
You cannot tell when a modern slot machine will hit because the outcome of each spin is random. No matter how many times a machine has spun, and no matter what the outcomes of those spins were, the probability of the next result remains the same. But people often believe otherwise.