Minutes an agent is given to come online, counted from the moment provisioning was requested rather than from the moment EC2 reported the instance as launched.
Leave this at 0 to disable the grace period, which is how configurations behaved before this setting existed.
When the grace period expires and the agent still has not connected, the outcome depends on Discard agents that never come online: either the instance is terminated immediately, or the idle termination clock starts running from the grace deadline so that a slow but still expected agent gets its full idle window.
This timer is independent of the launch timeout, and whichever of the two expires first wins. Setting a grace period longer than the launch timeout will not extend the launch timeout: the instance is terminated as soon as the launch timeout expires.