IMO, I suspect EM thinks that SCTY will hit FCF + in the next 6 months (likely Q4 as guided by SCTY). The shareholder voting process does take time to send out the votes, give the shareholders time to decide and submit their vote, then count the votes. This is usually done through paper mail anyways and could take over a month to get through the whole process.
When asked about why now instead of in 2 years, he went on to mention synergies in developing the integrated energy product and how this whole process would be accelerated at a rate not possible as separate companies.
A bit later he mentioned that down the road, like not far down the road as in next year, these numbers to acquire SCTY would look rather small.
IMO, if the reason in Elon's mind to do this now is to build this integrated energy solution at an accelerated pace for a favourable price. With about 6 months until SCTY is guiding to hit FCF+, and the gigafactory launch party in just over a month, and ramping TE, timing seems quite reasonable. Would've been nice to hold off until after Brexit and Q2 deliveries to lower overall uncertainty, but here we are.
EDIT: Elon just reiterated that since he's a large shareholder (>5%), they have to alert other shareholders at the start of the process. He says they will do their DD and everything else necessary for the process as it goes on and have done the required things before the end. Time is not really on their side, as I believe they want to have this whole product integrated and ramped alongside the Model 3, and they may not see such low prices on SCTY in the future (especially if SCTY is FCF+ in Q4)
