For attended operation sessions only, both client and server computers need to connect to a session within a specified period of time. This timeout period is defined by your Platform administrator; the timeout period is also shown in the System Configuration page of the Administration Application - Access Message Timeout property.
For unattended operation sessions, only the client computer needs to connect to the session within the specified timeout period. The timeout period does not apply to assets running Access Remote or Desktop Server because those assets may not be online yet, or they may have lengthy poll rates.
An additional parameter (Access Session Timeout) determines how long inactive sessions created for attended operation remain on the Platform before they are deleted.