It's certainly a mind-bending topic. I'll attempt to explain to the best of my ability.
One way to look at it is, from a certain hyperdimensional perspective, it's all happening simultaneously, and there are several disparate branches of a timeline that are possible, based on life-altering decisions, or something as small as the flapping of a butterfly's wings. Until things have happened and are "present", the future is open, but once they have happened, they are set in stone, because "time" as we know it, that is, past, present, and future, are all an illusion. There is no time, there is only what is present.
From the Lizzies' perspective, they're not going "back" in time, they're just going to certain specific space-time locators and manipulating events in such a way so that at the end of the time cycle, which is apparently within the next few years, they are able to reap the maximum harvest in terms of soul energy.
Also, these C's transcripts may prove informative:
Session: 970104
A: Deja vu comes to you compliments of 4th density STS.
Q: (L) Is deja vu a result of some sensation of the universe having
changed?
A: Or... some sensation of reality bridging.
Q: (T) As you move into the new one, you have leftovers?
A: No.
Q: (L) What is reality bridging?
A: What does it sound like?
Q: (L) Is it somewhat like merging universes? (T) A bridge is
something you put between two things...
A: You wish to limit, wait till 4th density, when the word will be
obsolete!
Q: (L) That still doesn't help me to understand deja vu as a
"sensation of reality bridging." Is deja vu because something comes
into our reality from another?
A: One possibility..
Q: (T) Didn't we talk about this? That it is a bleed through from other
dimensions... that when we think we have been someplace before, it
is because in another dimension we have...
A: Yes.
Session 970104
[...]
(T) It is like a program loading onto a computer. Some programs just
load straight in. Others need to create a space on the hard drive to put files that they need to
LOAD the program, but are not PART of the program, and when it is finished loading, it
erases all the "loading instructions." The hard drive is still the hard drive, but for a time,
the program used a sector of the hard drive, and created a temporary dimension, let's say.
(L) Is this what we are looking at here?
A: Close. And remember, we said "true" dimension!
Q: (L) So, it is like one hard drive, many programs, loading instructions for new programs
that are then erased, etc. If there is one "true dimension," and infinite universes within it,
does one particular universe exist, of and by itself, at any given time, until it is merged into
a new one, or is there within this one true dimension, multiple universes as real as ours is,
to which we could go, and could be there alongside ours, so to speak?
A: Yes to the latter.
Q: (L) And, can infinite numbers of "dimensions" exist within each level of density, even if
temporary?
A: Yes. If you want to go back and change "history," either for individuals or for universal
perception, you must first create an alternate universe to do it. Your 4th density STS
"friends" have been doing this a lot.
Q: (L) If you, being a general term, create an alternate universe, does the former one
continue to exist, or does the former one merge into the new one?
A: Both.
Q: (L) If the former one continues to exist, does it exist and evolve on its own,
disassociated with the second one, or this offshoot?
A: Clarify.
Q: (T) The universe you are in: you are going along and say, "I think I will create a new
Universe." You do it, and move to it, and you bring your universe with you. That is the
merging of realities. But, when you move to the new universe, you are no longer in the
original one which continues along on its own. The pattern of the old universe, you bring
into the new one, and when you become part of the new universe you have just created, you
are no longer part of the old one you just left. It just goes along with everybody else there.
(L) Is this correct?
A: Sort of... remember, one can create all ranges of types of alternate possibilities.
Q: (L) So you could create a new universe with a new "past," even?
A: Yes.
Q: (L) So, in that way, both actually occur and you can change the whole thing?
A: When merged, the former never existed.
Q: (T) Not for the person creating the new universe, but the former will continue for
everybody else.
A: Close.
Q: (L) So, for the person creating a new universe, the former never existed, but the other
beings who are satisfied with that old universe, and "go" with it, are still continuing along
as though...
A: Your 3rd density mind restrictions limit the scope of your comprehension in this area.
[...]