See choosing a time frame depends upon the trading style you opt. its not mandatory that you stick to one time frame, you would need to switch the time frames to get a better picture of the instrument. Smaller timeframes give you the current picture and larger time frames provide you a long term approach. So if you are scalping its better to use minutes timeframes I personally prefer 5 minutes to 10 minutes. when I am about to close the trade I cross check on 1 minute time frame and decide my exit point.