The connection timeout cannot be configured. It is hardcoded to 10 seconds in the mobile application.
The timeout is managed in Const.java (constant CONNECTION_TIMEOUT).
However if you are talking about the connection error after rebooting the device, this is another story. Headwind MDM retries to connect to the server within 15 seconds after it gets an error. This time is also hardcoded (helper/ConfigUpdater.java, line 156, find 15000 in this file).