KV = 60s
Documentation says KV takes up to 60 seconds to be globally consistent.
Changes may take up to 60 seconds to propagate
Cloud Storage = 0s
If you need a global strongly consistent store you probably want to look into Google Cloud Storage, which uses bits of Google Spanner since 2018 :
Cloud Storage now provides strong consistency
…With one big drawback: Google Cloud is unaccessible from China.
Edge caches : 10s
Not tested, but I was asking myself the same question:
If you need to stick with KV Storage because China, you might try to reduce the consistency lag to 10 seconds.
When you write in KV, use CloudFlare API to cache the data in all your CloudFlare Edge CDN, so they all will be warmed, and consistency will be achieved in 10s. Just like a regular deployment.
Check the source code of wrangler to see how a deployment works.