How long does it take the 2nd gear kevlar band to "seat"? Just had trans rebuilt and it won't chirp 2nd. The builder said that it had to seat and then it would shift harder. Is this correct?

I would find another builder...
Kevlar bands... :(

good luck.

I would find another builder...
Kevlar bands... :(

good luck.

Please explain so I can question him.

Kevlar material doesn't belong inside a trans. Great for ballistic protection but not what you need for a friction material.
It tears up the drum surface it is riding against, is known to flake off and contaminate the trans, and isn't necessary.

The Alto Red wide band works well in the 700 but needs a new or resurfaced drum to work with.

Ask him is he re-surfaced the drum or if he expects it to "wear in".

Kevlar material doesn't belong inside a trans. Great for ballistic protection but not what you need for a friction material.
It tears up the drum surface it is riding against, is known to flake off and contaminate the trans, and isn't necessary.

The Alto Red wide band works well in the 700 but needs a new or resurfaced drum to work with.

Ask him is he re-surfaced the drum or if he expects it to "wear in".
Wow, that doesn't sound good. He expects it to "wear in" THEN it should shift hard like I wanted it to.
I'll ask him about surfacing the drum.

Kevlar is hard, it will wear the metal of the drum.
It doesn't have as great of a co-efficient of friction as other materials. So it will slip a bit more than a good paper based friction on apply.
It will take more heat, but it creates more heat because of its design.

It just doesn't belong in an auto trans. I don't know of any reputable builders who actually use it. I think it is a sales gimmick by some.

If your trans isn't shifting as hard as it should into 2nd, you either have a too small servo apply area, not large enough orifice in the plate, low pressures, too short band apply pin, or other problem.

It is EASY to make a 700-r4 shift hard to 2nd, it actually takes some thought to figure out how to keep one from shifting too hard when you do most common valve body mods like increase line pressure, install larger boost valves, etc.
If yours isn't shifting firm, I would take it back and have him check the TV cable adjustment and if that is OK the line pressures with a gauge.
If all is well there, tell him to fix it.
It will shift as hard on the first shift as it ever will if it is right.