After the 30 day grace period the network is shutdown. You can add a new license at any point after this.
Licenses start to "burn" when they are shipped/emailed to the purchaser. So, if I buy 100 AP licenses today and the order is processed tomorrow and the email is sent tomorrow that's when the license activates/starts to burn. So, it's advantageous to not sit on purchased licenses and apply them as soon as they arrive.
Ryan / Meraki SE
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