[claw]

I googled chelating. I get the whole concept,but how long does this process take? Minutes? Hours?

[Borek]

Depends. EDTA with Zn²⁺ is fast enough to be considered instantaneous for procedures like titration. EDTA with Al³⁺ is much slower, which is why we use back titration:

http://www.titrations.info/EDTA-titration-aluminum

Short answer: there is no single answer.