I'm not sure why you would be late for an LLSP since you can book the time when you schedule it . . . however . . . if the reason you think you might be late is that you have an ADR and you're wondering what will happen if your meal takes a long time, then that is no problem.
ADRs take precedence over LLSPs. Just keep your receipt from the restaurant and if the entry point at your LLSP doesn't turn green, show the receipt to the CM at the tapstile. You will be let in.