****ing my business

I called consultants and they are all given me different excuses which contradict each other. I want to know why does Standard to Standard payments do not reflect immediately, the best if after a few hours but mostly is the following day. Clients pay using a standard bank account and expect me to buy materials and deliver same day but payments reflect only when they want to. I can understand payments from other banks because they can do a pay and clear now, but standard bank to standard bank does not give the option for pay and clear now.