there are edges at all timeframes

market is fractal. which timeframe one operates on depends on his/her

1. risk tolerance;

2. commission cost structure;

3. how hard you want to work.

there are HFT firms that do not hold for more than a few seconds. many of those firms rarely have a losing day. i have different positions open at all time, some for 15-60 minutes, some at daily frequency, and others are swings that can last 2-4 weeks.

just my 2c.