If the proof of concept takes an hour to code up, or proving the market exists just takes a bit of googling, then sure, you can prepare that before the first meeting where you suggest the idea.

If the proof of concept requires spending a few days in the machine shop making jigs and parts, purchasing equipment, and a custom PCB, then I really hope you'll bring it up for discussion beforehand in a meeting. Ten minutes of discussion with colleagues might be as useful as several iterations of prototyping. Not so that they'll shoot it down, but because someone might say "oh yeah, we have a spare mcguffin from last year's demo that you can use, should save you lots of time."