Rate of change measurements can be made for any period of time and can be based on hourly, daily, weekly, or monthly data. In my own work, I frequently employ daily closing prices of key market indices or levels of the advance-decline line (a cumulative total of advances minus declines on the NYSE or on Nasdaq) as my data stream.
I have found ten-day rate of change readings to be helpful for shorter-term trading and 21-day to 25-day rate of change readings to be useful for intermediate-term trading. It is helpful to maintain both shorter- and longer-term rate of change measurements. Often changes in direction in the shorter-term readings presage subsequent changes in the direction of longer-term rate of change measurements.