A simplistic form of time-travel is invented that allows you to swap bodies with your past or future self temporarily, but only when both parties agree. As such, you can't travel into a past self before you became aware of the technology, before it existed or before the first time you agreed to trade some present time for some time in the future. There are other limitations, such as you can only trade places with a future self that occurs after the last future self you traded with (so if you trade places with yourself in ten years, you can't later than trade places without yourself 5 years from now but you can trade places with yourself 11 years from now). The reason for this is obvious - you can't travel to the past of a known future because then you could change the past of a future you that is known to exist and destroy them (by example jumping into a future before them and killing yourself) which would break the continuum. However, there isn't any risk of a future self killing themselves in their own past to destroy themselves because while they are in the past, their present essentially doesn't exist yet and the actions taken in the present only lock in the inevitability of their existence when they swap back, so the continuum can essentially white wash it as a suicide in the present rather than a self-murder from the future. You also can't jump to the same future or past twice, it's a one time only usage.
The continuum is fairly self-regulating though and so seemingly obvious abuses such as trading stocks when you know the outcome are self-regulating with a sort of future-past-future feedback loop that rounds things out as the information flows forward back and forward again in an endless cycle.
Lots of interesting things such as people not being able to jump to their future selves and wondering why don't agree to it in the future or if they got killed or otherwise made unable to jump back. People chrono-touristing back to earlier lives to spend time with friends that were killed.
Think of the concept as a bizarre two-way version of the phenomenon in the film "The Butterfly Effect" but with more rules and tourism mixed in.