You attach this item to a vehicle. Once attuned once every 7 days you can create a portal from the vechile to a different point in time that is big enough for the vechile to go through. How close you get to the correct time period depends on your familiarity with it. As shown on the table below:

Familiarity. 

"Very familiar" is a time you have been very often, time you have carefully studied,  or somewhere you have vivid or fond memories of. "Seen casually" is sometime you have been more than once but with which you aren't very familiar. "Viewed once" is a time you have been once, "Description" is a time which you know through someone else's description, perhaps from a history book.

On Target. Everything  that enters the portal appear when you want to.

Off Target. Everything that enters the portal go to a random time off target. The length of time off target is 1d100 percent of the time that was to be traveled (rounded down). For example, if you tried to travel 120 years, landed off target, and rolled a 15, then you would be off target by 15 percent, or 18 years. The GM determines randomly whether you travvled to before the target of after the target time. They roll a d20 odd for past, even for future of the intended time.

Mishap. The time engine's unpredictable magic results in a difficult journey. Each time travelling creature and object takes 3d10 force damage, and the GM rerolls on the table to see when you wind up (multiple mishaps can occur, dealing damage each time).

Notes: Requires attunement