Why do you ask?

Trusses are typically designed to span from outside wall to outside wall and do not rely on interior walls for support.

Our house has sat with no progress for almost two weeks. Our builder claims it’s because it is better to wait on framing the second floor interior until the trusses are up. Curious if his reasoning made sense or he was just trying to cover up not making progress. House is already going to be 9 months delayed from the contract completion date so our skepticism is pretty high.

We just recently built a house owner/builder. Our interior walls were up before the trusses, but like PPF stated above, the trusses sat on the exterior walls for support and didn't need the interior walls. That said, I designed the house to have a very simple roof. If you have a complicated roof, you might have some interior bearing walls which means some of your trusses have to sit on the interior walls for support.

The other problem could be that due to the current building boom, truss manufactures are really busy. Last year, our trusses were almost 4 weeks delayed. I think this year things are worse.

The only walls needed before trusses are the load bearing walls. These are always exterior walls. Depending on design, there could be some interior load bearing walls, but this isn't common, especially with spec tract and builder's houses.

It's true that you don't need interior walls to put up trusses, but I also think your contractor is blowing smoke to cover up the fact that he's making slow progress. Why does he say that the trusses aren't up yet? It's not like they're a surprise element in the build....

Exterior walls framed, then trusses. Interior walls can actually get in the way of swinging them up if they are using manpower and not a crane.

No. In fact, you don't want a tight connection between interior walls and truss ceilings to offset the effects of truss uplift.