Federal regulations (created by the executive) are technically different from statutes (created by legislators), but there can certainly be criminal penalties f

Federal regulations (created by the executive) are technically different from statutes (created by legislators), but there can certainly be criminal penalties for violating them. I wouldn't be at all surprised if that were the case here, given the public safety implications of medical testing. The letter says that Theranos must provide "acceptable evidence of correction documenting that the immediate jeopardy has been removed". "Has been" is past tense, so Theranos really is required to fix the problems (at least the most serious ones) in ten days, not just plan to fix them.