For each page, you can set `fallback: 'blocking'`. If set, the page is not built at compile time. Instead, it will be compiled the first time it's requested. So the first request will take longer, then after that it'll be fast.

Alternatively, on a per-page decision you could decide to use server side generation (page built at compile time) or server side rendering (page compiled when requested).

You have options that let you spread out the time, but ultimately it's going to take time to build millions of pages.