wc to get character count of a file but exclude the initial characters of each line and the first line of the file?

I have some text files the looks something like this: Introduction and some meta data [00:00.000 --> 00:04.380] Lorem ipsum dolor sit amet, consectetur adipiscing elit. [00:04.980 --> 00:07.200] Sed mattis varius ligula vel egestas. I want to count the characters but exclude the first line and the time stamp, that is, only count the characters in Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed mattis varius ligula vel egestas. The length of the timestamps varies (there might be hours as well, in the example above it is just minutes). How do I do this?