Does the water always come through the ceiling in the same room?
No. The water follows the framing and the gravity, so the stain can appear several feet from the spot where the water got under the roof. The tracing is what locates the entry point.
Rafters and joists act as channels. A leak at the eave can run along a rafter for many feet before it drops through the ceiling, and the stain shows wherever the water finally comes out. That is why the technician follows the wet insulation and the frost rather than the stain alone.
In houses with plaster ceilings the water can sit between the plaster and the lath for a long time, and the first sign is a soft or bulging area that looks harmless. The readings are taken across the whole ceiling, not only at the stain.
What should a homeowner do about the roof and the insurance claim?
Roof repair and ice dam removal are separate from the water work. Photographs, the date of the thaw and the record of the wet areas are the things to keep for the insurer.
A roofer should inspect the roof and the eave, and any work on the shingles, the underlayment or the ventilation is quoted by that roofer. Ice removed from the roof should be done with care, because a damaged shingle is one more path for water. The restoration record can say where the water came in, and that helps the roofer find the same point on the roof.
Insurance treatment of ice dam damage depends on the policy and the insurer, and the cause generally drives the decision. Keep the photographs, the readings and the list of what was removed, and read the insurer's written decision before any finish is replaced.
How long does drying take after an ice dam leak?
Drying runs until the insulation, the framing and the plaster reach their dry goal. Because the water is trapped in the wall and the attic, drying often takes longer than the stain suggests.
The attic insulation is often the slowest material to dry, because it holds water in its fibers and it is hard for air to reach it once it is compressed. Where the insulation is removed, the framing beneath it is dried directly. The equipment comes out when the readings are back within range, not when the stain has faded.
A ceiling that is closed too early can show a stain again within weeks, and the readings are the only reliable way to know whether the cavity is dry. The plan says what dry looks like for each material.