@ralfswan Welcome to the forum!
I’m not sure if I really get what you mean. In a JSON export, item dates should already be included there (see this feature request (completed): ✅ Extend JSON export to include PW history and item dates).
In the very last sentence of this Export Vault Data | Bitwarden paragraph, you can have a look into a JSON sample, how it should look like.
If you not only mean the export, but the general “vault” view via the apps, then I think you might have a look into this feature request: