5 to 10 billion years.. Why even bother thinking about it on such a distant scale? Thats about twice as long as our planet has been around. Furthermore the sun is expected to render Earth uninhabitable in 1.4 billion years due to natural solar evolution. A galactic collision that far off will be something for a drastically different civilization who possess far greater knowledge and technology and inhabit distant worlds, or maybe no living beings will be around for it.