Actually found these for a non pond related project but thought they might work good for a DIY rdf application.
https://store.ezautomation.net/Time-...elay-s/486.htm
If you are using a float switch they have a Single Shot timer that when it sees a switch signal it will turn on for a set amount of time and then turn off until another signal is detected. The timer can be from 0.01s up to 999 hours.
If you just want to have a preset cycle time they have a cycle timer.For $50 its a handy device. And its made in the USA if that is something that's important to you.When input power is applied at startup, the Relay output is energized and the TON timer begins. At the end of the TON time, the output de-energizes and the TOF time begins. At the end of the TOF time, the output is re-energized and the cycle repeats as long as power is applied.