It seems that I am not the only person that feels the 90-Minute window is a good length of time to try out a game as Steam appears to be testing out 90-Minute full game demos. Currently the only game that has this option is the Dead Space Remake. You have to go to the game’s steam page, but you will see the option to “play now” and it will show you how long you have left on the demo.
Steam/Valve have not officially announced the new demo style and (as mentioned) it is only available for the Dead Space remake. The demo style could be a simple test and a way to offer a real in-game experience to people without going to too much effort. It also relieves the developer of the challenge of making a custom demo for people to play (which are usually not good examples of the game anyway). The demo also coincides with a 20% discount, which is a great marketing move. Both the 90-minute demo and the 20% discount expire on May 29th. The simplicity behind this type of demo makes me think that we can expect to see this pop up on other games in the future.