Why do you want to use circshift? That would put some of your last samples first! That's not the way to go about this.
To do this right you have to calculate the number of samples that corresponds to your requested time-shift, that is you have to take your sampling-frequency and calculate how many samples corresponds to 1.9e-12. If that is a full number of samples then you know how many steps to circular-shif with. BUT: Then you definitely have to crop out that number of samples to avoid including the product between samples from the beginning and end of the time-serieses, how to do that you can rather easily figure out if you take a small toy-array with say 10-15 elements and look at where samples end up after the circ-shifting.