4:2 Immediately I was in the spirit; and behold, a throne was standing in heaven, and One sitting on the throne.

Immediately I WAS in the spirit;

Humans are bound physically by time and space. So this "spirit dimension" is unique and not common for man. It is, however, the dimension(s) in which God moves. The transformation into this dimension happens immediately.

Paul had a similar experience in 2 Corinthians 12:1-4. When we are caught up to meet Christ, it will be instantaneous too (1 Corinthians 15:51-52).