It’s not a precise comparison, but let’s consider, for a moment,
the “pluperfect” construction.
- I had taken a shower when the doorbell rang.
Compare to the past tense:
The “pluperfect” is the “past past”, which is to say that you’re
talking about some point in the past, but referring to an event
that is even further in the past. At the (past tense) moment the
doorbell rang, you had taken a shower. The shower is even further
into the past than the past to which we’re referring.
If I had said I took a shower when the doorbell rang, that would
have been a different statement — that the doorbell rang, and then I took a shower.
turns on shower
Now, to your example:
- Thanksgiving was in four days, and Peyton had a feeling
she was going to miss it.
This is a similar construction. You are referring to a
specific point in the past, at which Thanksgiving was four days in
the future. It’s not four days in the future right now, but it
was at the time to which you are referring. If the “pluperfect”
construction is the “past past”, this is the “past future”
If there’s a specific grammatical term for this construction, I
don’t know it, but it may be something called the “past