A: I've found a workaround (see below). But this delay is by design: If an application or update is being deployed to thousands of machines, and all of the machines hit the distribution points for the download at the same time, the servers and network could get overloaded. So each client adds a random time of up to two hours to the installation specific deadline time. This staggers the download of all the clients as documented at the Microsoft article "Operations and Maintenance for Software Updates in Configuration Manager" (under "Deploy Software Updates"/ "Automatically Deploy Software Updates"/ "Create an Automatic Deployment Rule"/ "To create an automatic deployment rule"/ "Step 8"):

"Installation deadline: Select one of the following settings to specify the installation deadline for the software updates in the deployment:

As soon as possible
: Select this setting to automatically install the software updates in the deployment as soon as possible.

Specific time
: Select this setting to automatically install the software updates in the deployment at a specific date and time. Configuration Manager determines the deadline to install software updates by adding the configured Specific time interval to the Software available time.

Note: The actual installation deadline time is the displayed deadline time plus a random amount of time up to 2 hours. This reduces the impact of all client computers in the destination collection from installing the software updates in the deployment at the same time."

This random additional time isn't configurable. However, I have found a workaround if you must have all computers targeted install the application or update at the specific time exactly.

The solution is to set a maintenance window for the targeted machines, and set the installation deadline at least two hours prior to the maintenance windows. For example, if I want everything to install at 6 a.m., I just set the deadline of installation for 4 a.m., and then I configure my maintenance window for 6 a.m. With this configuration, everything installed at 6 a.m. exactly.