Dishonored 2

[Kreekakon]

There is also a timepiece gimmick in the game which allows to see different time. I don't understand if the engine is instantly streaming retextured level and how to code this.

Off the top of my head, the way I would "try" tackling this sort of effect is by having two environments (One for each time period) in the level each with a player controlled camera. When the player moves or looks around, he will control both cameras so that their view is synced. Turning on past view or even switching time periods would be a result of interacting with the other player in the other environment.

Making it mechanically work should be fairly simple. The tricky thing is making it look nice and making the transition smooth.