Blindvalet.com is a free web app that works great in desktop Chrome. Ultimate Holdem Timer is a free chrome app that I use on phones or tablets with good results. Give both of those a try with your chromecast and let me know. I've been trying to cook up a solution for a TV blinds timer that works on a RaspberryPi and still haven't gotten there yet. I'd buy a chromecast if there was a solid solution.
How easy is it to connect a chromecast to a new wifi network? Ultimate Holdem Timer, a compatible phone, a chromecast and a charger is a really portable solution, assuming the host has a TV in the room and wifi router already.
Super easy to configure, just use the Chromecast app.
I do screen casting from my Nexus 5 all the time. It will occasionally lock up but is reliable most of the time. I like the suggestion of Blind Valet via Chrome browser. That way, I can use my phone during the game.