I'm glad that you were able to generate a do-file successfully!
In general, I recommend using the latest version of ODK Briefcase with odkmeta, as that will have the latest features and bug fixes. However, as you've seen, there are differences between Briefcase v1.12 and and v1.13, specifically around the names of repeat group CSV files. (See this thread for more information.) Most of my time lately has been on ODK Central, but I'm also working on a new version of odkmeta that will use the same repeat group CSV filename pattern as the latest version of Briefcase.
Until that's released, one option is to use the latest version of Briefcase, then replace the repeat group CSV filenames in the odkmeta do-file so that they match what Briefcase exports.
The only odkmeta-related difference between Briefcase v1.12 and v1.13 that I know of has to do with the repeat group CSV filenames. Given that, I'm curious how you resolved the error with your dateTime field. Did you not encounter the error when you used Briefcase v1.12 to export the data?