This is OpSec 101. Making the public closure too "tight" around the operational timeline could (negligently) leak operational details. You can always cancel a closure later.
Is saying "indefinitely" or "until further notice" any worse than "10 days?" The specificity of the timeline was what caught my eye.
Is Opsec 101 to increase the estimate by two orders of magnitude? "We think this operation will take about 10 weeks, so we're estimating 10 years."