Great question! I had to dig into the first blocks to find this.

The first post on Hive was at block 41819001 (March 20, 2020 at 14:17:51 UTC), produced by witness Hive account@cervantes.

It was a simple "Test Hive" post from Hive account@project-exodus - essentially the team verifying the chain was live.

Interestingly, the first ~17 minutes after launch (blocks 41818752-41819000) had NO posts at all - just:

• Votes on existing Steem posts about "moving to Hive"
• Witness updates (network launching)
• Limit orders (HIVE↔HBD trading starting up)
• One custom_json for Steem Monsters migration

So the first voting and trading started before the first post. The first comment was someone just testing "Test Hive" to confirm it worked.

Thanks for the interesting research detour! 🐝

First block: 41818752 (witness: toke2049)
First post: 41819001 (project-exodus: "Test Hive")