On Linux when we read the time zone data files, we support parsing the POSIX format for specifying the adjustment rules. e.g.:

std offset[dst[offset][,start[/time],end[/time]]]

http://man7.org/linux/man-pages/man3/tzset.3.html

The "start" and the "end" in the format can be specified by Julian day. one format which we support is "Jn" but we don't support the 'n' Julian day format. The reason is we didn't encounter this case so far and also, we'll need to handle this as a new rule type. we have this issue to track supporting 'n' format.

https://github.com/dotnet/coreclr/issues/17393
dotnet/coreclr#17635