Ideally, using a cloud-based service means you don't have to worry about downtime or update processes -- but when that cloud service is being used to manage desktop devices, that's less likely. The next update for Microsoft Intune will involve a 10-hour downtime and require client devices to reboot.
The update is broadly synced with the October release of Windows 8.1 and Windows Server 2012 R2, but existing customers will see staggered rollouts prior to that date.
Exactly when the downtime happens depends on where your service instance is located. For Asia-Pacific sites, that could be anywhere between 26 September and 17 October. Subscribers will receive an email confirming their upgrade time one week in advance.
Hit the Microsoft post for full details of the downtime. The upgrade adds support for Windows 8.1 and a couple of other tweaks.
Intune Service Upgrades Begin September 23rd [Windows Intune Blog]