Depends on how it works.
Let's keep it simple and use following model, let's say the backwards machine goes 25 years back, and the other 25 years forwards.
|CURRENT TIME[<=[You=>]]|. If physics say that both machines are activated at the same moment it would mean that the first machine would go backwards and you in the other machine go forwards, giving following result:
[<=] |Current time| [YOU=>]
However if the machine you're in is activated a moment later than the backwards machine, it would mean that you are send backwards in time, then forwards in time. Meaning that you would do the following= (Current time - 25 )+25. In other words: you would stay in the same spot.
Resulting in this:
[<=] |CURRENT [YOU=>]|
I hope this made more or less any sense?
What event in your life had the biggest influence on you?