Spider-Man: Across the Spider-Verse takes place over a year after its predecessor. As we have seen an older-looking Miles Morales in the trailers for Across the Spider-Verse, it does seem like a time jump has taken place.
Now, thanks to Christopher Miller, a writer and producer of Spider-Man: Across the Spider-Verse we have precise information on how big the gap is between the first film and the sequel. According to Miller, there is a year and four months between Into the Spider-Verse and Across the Spider-Verse.
<social>https://twitter.com/chrizmillr/status/1650703386868858881</social>
Miller didn't give any reasoning behind this specific timing, but fans on Twitter are speculating as to what it could mean. Hopefully, with the film set to come out in June, we'll have a better idea on the relevance of this time jump soon.