Our delta crawl runs hourly and checks the post date in the sitemap to index the new/updated posts. The ‘lastmod’ field in the sitemap must be later than the last indexed date for delta crawl to work.
But any deleted URL(s) from the sitemap need re-indexing to avoid displaying the deleted pages in search results.
SearchIQ has an infrastructure that can handle billions of searches per day. So, we want our clients not bothering by this when they use our service. However, if your site is at high volume and you should consider to use our paid package that comes with better SLA.
Document limit is applied to Account level. However, we give you good buffer if you are not too far exceeded your account limit.