Bitcoin Android Official Wallet

[PeRo]

I set the fee to economic. I am wondering how much time will it need to arrive to the other address. And also, do I need to keep the Bitcoin Wallet app open or can I continue the transaction in the background with internet? OR can it send while the screen is locked, but I left the internet and the app open?
I'm using the Official app from the Playstore by Bitcoin Wallet Developers.