20 min is an odd timeframe. How well does it work ?
The indicators work on per candle drawn. I use Bollinger 20,1 - essentially, meaning the price deviation of 1 Standard Deviation on an average of 20 data points. I need a look back of at least 1.5 days to decide on the trend and anywhere between 1.5x to 2x the minimum data points required. Hence this period - it works for me