Client Behavior with Update Deadlines
You can specify a deadline when you approve an update or set of updates on the WSUS server. Setting a deadline will cause clients to install the update at a specific time, but there are a number of different situations, depending on whether the deadline has expired, whether there are other updates in the queue for the client to install, and whether the update (or another update in the queue) requires a restart.
Expired and unexpired deadlines
If the client contacts the server after the update deadline has passed, it will try to install the update as soon as possible. WSUS administrators can set update deadlines to a date in the past in order to have clients install the update immediately.
If the deadline has not passed, the client will download the update and install it the next time an install occurs. For example, if the client downloads an update with a deadline of 6:00 A.M., and the scheduled installation time is 3:00 A.M., the update will be installed at 3:00 A.M. Likewise, if a user starts an install before a (downloaded) update's deadline, the update will be installed.
Deadlines and updates that require restarts
Updates that have deadlines and require restarts will cause a forced restart at the time of the deadline, no matter when the update was actually installed. For example, if an update with a 6:00 A.M. deadline was downloaded and installed at 3:00 A.M., but the computer was not restarted at that time, it will be restarted at 6:00 A.M.
Moreover, if the computer is pending restart (because another update requiring a restart was installed, but the computer was not restarted), and an update with a deadline is installed, the computer will be restarted. The following is an example of client behavior with an unexpired deadline:
Update 1, which has no deadline but requires restart, is installed at 1:00 A.M., and the computer is not restarted.
Update 2, which has a deadline of 6:00 A.M. and does not require restart, is downloaded and installed at 3:00 A.M.
The computer is restarted at 6:00 A.M. (the deadline of Update 2).
The following is an example of client behavior with an expired deadline:
Update 1, which has no deadline but requires restart, is installed at 2:00 A.M., and the computer is not restarted.
Update 2, which has a deadline of 1:00 A.M. and does not require restart, is downloaded and installed at 3:00 A.M.
The computer is restarted after Update 2 is installed, at 3:00 A.M. (the first possible restart time).
WSUS updates and deadlines
A WSUS update (an update that is required in order for WSUS to continue functioning correctly) has installation priority over other kinds of update. If an update with a deadline is blocked by a WSUS update, the deadline will apply to the WSUS update, as in the following sequence of events:
Update 1, which is a WSUS update with a deadline of 6:00 A.M., and Update 2, which is a non-WSUS update with a deadline of 2:00 A.M., are both downloaded at 1 A.M.
The next scheduled install is at 3:00 A.M.
The install of Update 1 starts at 2:00 A.M.
If the deadline of a blocked update has expired, the WSUS update that is blocking it will be installed immediately.