Backup Error

Hi Fellow Forumers.

I just want to clarify something in Symantec Backup Exec 2012.

Backup Jobs are running after 2 hours it was failed. Stating that Agent for Windows is not started. My colleague incidentally stop agent for windows and forgot to start the services.

My Questions:

1. Is that normal it tooks 2 hours before the backup fail?

2. Why isn't the error occur during the backup started?

Need some explanation on this. Thanks very much.