I have a couple of questions or problems regarding date&time frames in id3 tags.
%RELEASETIME% / TDRL
mp3tag stores the field %RELEASETIME% into a TDRL frame, even in v2.3 tags. This id3 version does not have TDRL frames, thus a TXXX frame should be used instead. TDRL has been introduced with id3v2.4.? / TIME
The TIME frame of id3v2.3 is not yet supported at all.%DATE% / TDAT
Although it is supported, the %DATE% field is not properly converted to id3v2.4, imho. As far as i understand the spec the conversion should be TYER+TDAT+TIME <-> TDRC. TDRC is explicitly mentioned in the 2.4 spec as replacement for the deprecated v2.3 frames. mp3tag seems to convert TYER <-> TDRC and TDAT <-> TXXX:TDAT.