Is timing SEO plain stupid?

We’re opening a diagnostic clinic in about 14 months and want to start SEO early so that by the time we launch, we’re already ranking and attracting customers. The challenge: We won’t be offering services until we open, so we don’t want to create sales pages too early and have people land on them without the ability to book. But we also don’t want to start from zero when we go live. Local SEO and Maps SEO will be key, and we were thinking of building authority through building topic clusters relevant to our service. How long if we have some authority in the space would it take for sales pages to start ranking? Ideally, I want our sales pages to start showing for people with purchase intent 3 to 6 months before opening. Also, am I tripping with not wanting to rank for sales intent if we can't satisfy it? I guess I just want to be able to fulfil a potential customers need if they have one.. but maybe there is no reason for this precaution? Would love to hear from anyone who has experience with SEO for new businesses that need to rank by launch.