Hi altcoinUK,

I posted a rough draft of the 3D printed "prototype" enclosure from our "Industrial Designer".  This may look like an amateur attempt for what should be a professional enclosure for the IoT devices. This is not the case. This validates dimensions and usability/weather proofing techniques that need to be thought of at the very beginning.
When producing a final product, many stages of validation occur to reduce the final cost of output for a particular product that is manufactured.
It is absolutely necessary to produce a "prototype" prior to actually committing to manufacturing of the physical enclosure. Reduces risk and iterations that incur NRE (Non-Recurring Engineering) cost.

On another specific note, we have a pcb that validates each IoT device on a mesh network using hardware that has cryptographically signed information.
Here is the "rough" draft board design.



What this does, is provide a more difficult way of attacking a mesh network versus attacking multiple sensors within the network with a chip signing mechanism. 

You had asked about the time aspect of validation. If based on btc, there is a 10 minute delay...
When the Smart Contracts and Micro transactions functionalities are combined, this enables very fast data verification and validation with minimal bitcoin blockchain bloat.

If you have received quotes from other people in regards to time, I do not think they have asked you what type of IoT device that would exist in the mesh network to be able to respond accurately to your question.

In the case of our chip, it takes between 10-20 milliseconds to produce a signature that can be authenticated. Depending on the number of devices and their specific roles within the mesh network, this can vary considerably. We are working on datasheets that will accurately identify potential bottlenecks that pertain to the different type of devices and their roles in a mesh network for the IoT.

I hope this helps.

Regards,
ASIC-8Tile