Depends on who the delays hurt more. If Twitter can use in-house lawyers, it doesn't really add to their costs no matter how long it goes on for. Either the company gets $1B in cash, or their stock gets bought out at (currently) 50% above market value; seems like a win for them no matter what. Musk has a lot more to lose if they decide to make the process painful.
If he has to dump Tesla stock to make the deal go through, it will drive the price down; who wants to be holding when that happens? The lower the price of Tesla stock, the more he has to sell, which could lead to a rapid crash as investors try to get out before he has to sell.