I've heard @YakiHonne does scheduling. Note thought that drafts and scheduled posts are probably public somewhere on relay. So if this scheduling is about some big reveal of secret in the future, check if it is not saved in plaintext on some relay.
That isn't my concern. I tend to write long articles and write them ahead of publishing them on substack. I repost to nostr (hopefully nostr will continue to grow and I might go nostr only). Because my articles are long, I like to spread them out, otherwise they are likely to get ignored as too much at once. When life gets busy (like being out of town), it is nice to have them scheduled and have them publish on their own at the right time.