Judging from what is needed overall, how much has been done so far, and what's left to be done, my personal guess is June, at the earliest, for volume shipments to backers. July feels more likely.
This is because they need to build a stock of multiple products before most of the backer orders can be shipped. Starting volume production on one or two items isn't enough. Problems with one production line for one product could easily affect all shipments.
What experience do they have with volume production? They've done only prototypes, so far. New problems will arise when mass-production of each item starts.
If you add up all the hardware needed to satisfy all backer orders, they will have serious logistical problems to resolve. Another area in which they have no experience, and can't possibly make informed estimates.
My bet is that at least one shipment of 1000 (or whatever) units of one kind or another (Sensors, Relays, whatever) will be junk and need to be remanufactured or at least reworked. Which means all shipments needing one of those items will be held up, no matter what else they contain.
I'm assuming WigWag can't afford to do any labor in the US. So all rework will need to be done in China. Do you know what the round-trip time for that will be? It only takes one or two to derail any shipment schedule.
There is no way they can afford multiple shipments to each customer (extra shipping fees, extra packaging, extra handling). So it's an all-or-nothing game.
I'm betting "all" is at least 4 months away. And "nothing" until then.