I think your concerns are Valid. I'm a former Bruce Hardwood distr mgr. Its not as common to install a solid over radiant. I know its done, but goes against most industry advice. The wood needs to be within 4 -5% moisture level of the wood to the subfloor. Its not 'how' many days but what the moisture reading is when installed. At Armstrong we recommended that radiant systems be operated continuously for 7 days prior to installation and turned off 4 hrs before installation. Every radiant system is a little different. NOFMA has info on common shrinkage of wood. It depends on species and which part of the country your in. There is a chart which I no longer have but you should be able to find it online.

Thank you for your quick reply! I will check out the information and NOFMA.
I emailed the owner in the interim and have since spoken to him - he was on his way here and has now arrived. He told me that the wood was dried to a moisture content of 6-8%. He said that it has been in a heated building since then (either at the mill or his shop) He tells me the wood was kiln dried then went to the company that milled it then went to his shop (in first post I incorrectly stated that it was at his house) that has radiant heat where it was planed and has been stored. It was delivered on his truck and was not exposed to rain/snow.

The material that was delivered yesterday will sit over the weekend and will not be installed (until the earliest next Tuesday, so that would be 4 days). The material that was in the garage is what is being installed today.

I do trust this company and the owner to do a good job. They do very nice work and are respected in the community. He assured me that what was more important than just acclimation is the moisture content of the wood on installation. He noted that letting wood sit for a longer time wouldn't necessarily be the answer. That it depends on the condition it was stored and the moisture content. He said he did not do a moisture test but that the mill or the supplier (I can't remember which one he said) tested the wood for moisture content. How easy or difficult is that to do - and should I really expect him to do a moisture reading now?

Thank you again.

Yes, you should really expect him to do a moisture reading now. If I am reading your words correctly, it was dried in one place, the milled in another, then planed at a third place? That seems odd to me, but in any case it could pick up moisture anywhere in that process. My husband dried and manufactured our flooring at his own shop and sent it directly to the heated and climate-controlled job site, but we still "moisture-metered" it before installation.

what he is not mentioning is checking the moisture content of the subfloor.

The wood has to be acclimated to the job site , not where it is stored . for 2 1/4" strip the wood has to be within 4% of the sub floor for 3" or wider 2% then you have to take RH and Temperature readings and when they all fall in line then and only then is the wood ready to install . Time has nothing to do with acclimation .
You don't say how thick the wood is .
Had a customer wanted me to install 3/4" over radiant . Called Bruce . they said it would void their warranty .
I hope you have a outside thermostat on the heating system . NWFA Certified Inspector

PS: start making a paper trail by taking photos where the wood is being stored . dates of delivery and installation .
and any readings the installers take .
You will thank me later .

Solid wide plank is not recommended over radiant heat.