use POSIX;
print strftime("%FT%T%z",localtime)."\n"; # 2025-03-05T10:50:44+0800
print map "$`:$&\n",strftime("%FT%T%z",localtime)=~/\d\d$/; # 2025-03-05T10:50:44+08:00
Both formats are valid but the latter one looks better to me.