1031 Exchange questions

[Ben A]

I'm planning to sell a single family rental (5 yrs now) in CA and do 1031 exchange.

- At what point do I need to make the election to do 1031 exchange? How much time prior to sell?

- As I understand, part of the sale proceeds can also be used to rehab the exchange. Is this correct?  Is there a particular ratio of rehab money to total gain?

- Does the 180 days period still hold?  Is it 180 days from close of sale to close of new purchase, or to execution of new purchase?  What about the rehab time?

Thanks for any clarifications.