Reddit's native crosspost is different from sending a duplicate: it points back to the original submission, so I wouldn't assume a generic scheduler can queue that exact action. Check whether the specific Reddit tool supports native crossposts and whether each destination subreddit allows them; otherwise, schedule separate submissions and space them according to each community's rules.
For channels outside Reddit, I built PostOnce.to to crosspost or schedule your own content to TikTok, Instagram, YouTube, Facebook, X, LinkedIn, Threads, Pinterest, and Bluesky. Setup takes about 10 minutes, it can re-publish older posts, and there's a 7-day free trial. I keep Reddit's queue separate so the source post and subreddit context stay right.