it appears that %t and %z are already used by a bunch of programs, including the kernel:
term% grep -n 'fmtinstall\(''[zt]''' */*.c */*/*.c */*/*/*.c
cmd/trace.c:137: fmtinstall('t', timeconv);
9/port/edf.c:122: fmtinstall('t', timeconv);
cmd/db/output.c:159: fmtinstall('t', tconv);
cmd/vac/unvac.c:45: fmtinstall('t', mtimefmt);
cmd/venti/srv/fixarenas.c:1897: fmtinstall('z', zfmt);
cmd/venti/srv/fixarenas.c:1898: fmtinstall('t', tfmt);
--
cinap
