It's easy to think that "commence building by April 30" means we have to see cranes rising by then or they're toast. I don't think that's at all right. If they have a contract signed, even just for site work, and have commenced any staging at all, that will get them over the "commence building" hurdle.
I realize there's a bunch of footings in place, so that eliminates a lot of steps from the normal site work process. However, the logistics and staging to build this one will be wickedly complex, since they have to keep the station running - they will have nothing remotely comparable to normal site control. That means the negotiation with MassDOT and the resultant documents guiding site access will be wickedly complex, too, so I'm not surprised that they're getting worrisomely close to the edge.
And then when* they "commence construction", I won't be at all surprised if there are quite a few weeks where the only activity is pretty modest in appearance to the layperson - but actually pretty complicated to the engineers doing it.
*Using "when", not "if", without any sense for whether that's right. If I were betting, and allowed to keep my bet at a low and easily foregone value, I'd bet it's going to happen.
My response to the design is .... better than "meh", but not enthusiastic. I'd have liked something better for such a gateway location, but I won't hate it, either.