Nothing difficult but the right degree of knowledge is needed.

1) You need to read the system time in order to trigger the start of the function when desired;

2) You have to properly linearize the raw value of the level transducer, and return it to engineering units. When working with analogs you have to insert filters, remove any offsets, normalize and scale to get the engineering value correct.

Since the type of pumping used is not known for now, I recommend applying a decimator filter, a little strong, to the analog data because starting and stopping pump can cause fluctuations to the level measurement that would compromise the operation of the system.