While you need a stock that's moving, hence a volatile stock, that isn't the only criteria. Some stocks are heavily manipulated and some aren't. But the first hour and a half of the trading day are more consumer oriented and can be swayed somewhat. But the rest of the day is driven by institutions running computers with algorithms that have specific programmed agendas that you can't know. And if several of them work on a single stock it's choppy and unpredictable. The most predictable time of the day is an hour to an hour and a half after the bell.