E-6 Dilution

Sorry to post again today, but if I am developing E6 can I dilute to 1:1 to keep the chemicals longer? If so how long would that extend the dev times?

No.

If you want to save on chemical costs and still do one-shot, use rotary processing.

If you don't want to do rotary processing, reuse the developer with slightly increased times. It is hard to say exact values but it shouldn't be much. Maybe in a range of a few seconds per roll per liter. For example, Tetenal gives instructions for this.