If you have previous experience of working with MVC patterns and Java you can easily grasp the concepts within a week easily. Its follow the standard Controller, Service , DAO Architecture, You only need to learnt the syntax and other patterns such as Filters (Proxy), Injectors (Dependency Injection), Spring data ... etc to code projects in Spring which you can easily learn in 1-2 weeks or less.
Spring boot eliminates most of the configuration nightmares that you may face while configuring spring projects yourself. :P
Just Start !