Browse to Server Manager>Remote Desktop Services>Collections
You should see at least 1 collection here that contains the applications you are hosting as RemoteApps. Click the collection name.
At the top you should see a Properties section, to the right of it is a TASKS dropdown menu. Click this and select Edit Properties.
Select the Session section.
The Idle session limit setting can be changed to 2 hours here.
Below this you should also see a 'When a session limit is reached or a connection is broken' setting. Having this set to 'End the session' will completely end a users session after 2 hours, closing any open programs or processes opened during their RemoteApp session.
Setting this to 'Disconnect from the session' will disconnect the user but will keep their processes open until the 'End a disconnected session' setting time limit is reached.
These settings will effect all RemoteApps hosted within that Collection and anyone connecting to them.