Hi friends

I have some question about mtb shoes and clipless pedals:

how much practice i need to learn how to release my foot from pedals easily? can i make my foot free fast and easy when i''m loosing my balance or I should have and accident? (-:

can i use clipless pedals without locking my foot too?

i have much city usage too and i need to stop a lot of time, then is it hard to do this with clipless pedals?

Sorry for my bad english

Regards