How to Sell Specific Quantity in Specific Time Functionality

I am building an application for a company. I want to add some functionality in it but unable to understand how i can add it. 

I am selling 1 item just and i want to sell 30 Units per 3 Days for Specific Customer(Based on Unique ID). How i can monitor that this customer has taken the quantity or how much remaining quantity i can provide him/her. And After 3 Days if there is remaining quantity it must be 30 Again.

How i can store all this information in table and how i can make a check on the quantity and lastService date of the Customer and remaining balance ???

Kindly Guide me Step By Step.

Thanks

Jazaib