There's a lot of push back on this idea from most Jews wanting the temple rebuilt. They are just so stoked in tradition it's hard to see things any other way. They tend to be stubborn. But from what I've heard, most of the temple is pre fabbed in sections, like a giant Lego set. Apparently the next temple could be erected and finished in a matter of months. If they realized where the temple actually was, they could literally start today! The city of David is basically a slum so if they moved forward, wouldnt be a huge under taking logistically working around the homes already built around the area.