Is this limited time? If so, how long do I have to get it?
Is what limited time? The game? Nah, it's like any other game.
I mean the bundle. Are all 4 only going to be offered together at $60 for a short amount of time?
No. The 4 games are together permanently. They are one game as a whole with one combined user interface and achievement list.
It's similar to the Serious Sam collection, Hitman trilogy, or Orange Box game, if you've ever played any of those.