What is cheaper?
Set up a constant time of reaction and measure the concentration of the products or;
Set up a constant quantity of reactants and, with an indicator, measure the time until the reaction stops.
If you know another protocol, Can you explain it, please?
It depends on scenario.
If time is cheap, while measurement is expensive ( e.g.high fixed price for each value ), then constant time method is probably cheaper.
If time is expensive, while measurement cheap ( e.g. continuos measurement ), the constant products method may be cheaper.
