Hedera will be upgrading and restarting the testnet to version v0.7.0 (release notes:
https://docs.hedera.com/guides/docs/release-notes/services) on Thursday, August 20th at 17:00 UTC. The restart will take approximately two hours to complete during which time all network services will be offline. This upgrade should not affect your project's compatibility or data. As a precaution, we always recommend preserving project data prior to any testnet upgrade.