what you want to do can be referred to as SIP,i.e. Systematic Investment plan whose main purpose is to reduce the impact of volatility on your overall invested amount.Having said that logically the greater the number of investments the greater the DCA/SIP effect which would result in lesser impact of volatility.
Hence if you want to invest 120$ you must select 4$/day plan over 30$/week plan
but due to Maker/taker fees,taxes,minimum purchase amount  and other variables people cant always optimize this strategy.