@Zackery Martinez It also depends on what kind of loan you are using. With an FHA loan, there is a document called the "FHA Amendatory Clause" that is kind of a loophole for the appraisal contingency (doesn't apply to a conventional loan). But beyond that, I wholeheartedly agree with Grant above about checking with your lender. If you've already been fully underwritten, then a 12-day loan contingency period might be workable, and not too much of an issue. I wouldn't waive the loan contingency entirely, but if the lender is able to make it work and get you approval within 12 days, it's an aggressive counter from the seller but not uncommon. Also, depending on how the counter is written (check with your agent on this) the contingency doesn't "automatically" come off. You still have to submit a signed contingency removal form, so even at the 12-days or after, you can just not do it, and won't lose your deposit. You will probably get a Notice to Perform from the seller's agent, and then possibly lose the house/fall out of escrow. But you'd keep your deposit. But again, the wording matters here, so check with your agent.
Good luck man!