Because on Thursday after hours Tesla indicated that record date, subject to SEC review of the filings, will be during the week of September 19th. Since recall of lent shares allows institutions to assert their share ownership in order to vote, it need to be completed 3 days before the record date. Only entities that own TSLA shares 3 days before the record date are considered to be SH for the purposes of the vote and are allowed to vote on the acquisition.
I think you likely know this, but I just wanted to add a little detail for other readers.
A securities lender need only terminate the loan 3 days prior to record date. It doesn't need to actually have received the securities until the record date. The borrower is required to return the securities on the 3rd day after recall.
It's the same thing as any buyer/seller. E.g., if I buy shares today or tomorrow of either SolarCity or Tesla, I will be able to vote the securities even if the record date is on Monday since I will receive the shares on Friday or Monday (T+3). Similarly,
assuming the borrower performs*, I can terminate a securities loan (i.e., initiate the recall) as late as tomorrow and I will be okay since I will receive my shares back on Monday.
* The big question in my mind is what happens if the borrower doesn't perform. The lender's agent should start to buy-in after the 3rd day. However, if that happens, the borrower might not get the shares in time. Similarly, shorts should start to try and cover the moment their shares are recalled since they will be on the hook if the lender buys-in.
Reality check. Having continued to think about this, I'm not convinced the recall will happen. Although that's really only because mutual fund companies aren't as disciplined about governance matters as they are about investing.
What mystifies me more is why shorts would still be in this trade. The risk of a recall squeeze is real (even if it's unlikely) and they could get really burned. As a steadfast Tesla long, I'm likely not the best judge of whether shorts are intelligent, but I just don't understand this aspect. I would have been backing out of the short trade ever since the merger agreement was signed.
Now, for some strictly fun conjecture about a likely very illegal move.... Tesla and SolarCity could actually fuel a recall short squeeze by waiting to set the record date.
1. If they hear from their large institutional shareholders that they are having trouble recalling shares (this communication is probably the illegal part although I struggle to understand why), they could decide to push the record date to the end of the week and announce as such on Monday, the 19th.
2. This will allow those shareholders/lenders to force buy-in of their lent securities and still receive their shares in time to vote (e.g., buy-in would occur on Tuesday and squeeze would begin in force).
Of course, Tesla/SolarCity could have already set themselves up for that without any illegal shenanigans. By giving a range of a week for the record date, they allow lenders to wait until tomorrow to initiate a recall. On Monday, they announce that record date will be Friday, the 23rd. Buy-in happens on the 20th and lenders have actual Tesla and SolarCity shares on Friday.