You'd need both time travel and teleportation, or else you'll find yourself in space when you travel forward or back in time. The Earth isn't a stationary object
Actually, teleportation would be more powerful than time travel, since you can travel through different times as well with teleportation as an ability, but you can only teleport to a different time with time travel.
That entirely depends on what is being done when traveling in time. Is it localized, regional or defined at the time the lower is used. Does it effect the world around you or is it you in the world that is manipulated.
Depends if it's a monkeys paw power or a self defined ability