I buy on dummy bars or different reliable setups.
I hold till the previous bar is broken (usually 30 min charts, sometimes 15).
This can last all day (which I close position e.o.d) or can last 30 minutes, where my entry bar's low is taken out.
Maybe take 3-4 trades a day, but that depends on what the market overall is doing, usually.
I have very simple rules and a very simple strategy. I won't make thousands everyday, but I will preserve my capital. Sometimes I will make a thousand here and there.
If I disobey my rules, I can get hurt, badly, emotionally and financially.
It's more about you, your psychology, risk management, and discipline then entries/exits. imho.
once you find your style and follow your rules completely, you should be fine.
of course you need a reliable strategy, which there our thousands. See MaoXian or Trader-X.blogspot.com for what I look for.
hope that helps?