Hedera will be upgrading the testnet to v0.5.8 (release notes:
http://hedera.io/release-notes) on Monday, June 8th, at 17:00 UTC. This upgrade will take approx. 180 minutes to complete, during which time all network services will be offline. This is a re-scheduled patch from May 19th that addresses the resilience of peer-to-peer networking used in the consensus algorithm. An update notification will be sent via Hedera Status channels upon completion.