Unless you're running a server on localhost, you'll have to wait for the connection to time out. Better to use 0.0.0.0 which is an invalid address and will fail immediately.
Wouldn't you get an immediate "connection refused" for localhost, not have to wait for a timeout?
That's true on my phone but not my laptop. I would guess that most firewalls would just drop the packets.
Ghostery and the EFF's Privacy Badger are your friends. You will get better blocking as these maintain lists with all the alternate domains they use.