Earlier quoted context omitted.
Basically just use the output of `date -u`.
Use `date -u -Iseconds`, please ;-)
date: illegal option -- I
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ...
[-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]