Not that I'd be using something like this, but since the question came up in #zsh and I couldn't find any post listing the most sensible solutions, I decided to document the results.
In order to get a prompt that looks like
host – 13:33:37 user:~:%
just set your PROMPT variable to one of the following values.
Option 1: Use \n within $'' (that's two single quotes):
PROMPT=$'%m – %*\n%n:%~:%# '
Option 2: Use a line break within "":
PROMPT="%m – %* %n:%~:%# "
Option 3: Use $prompt_newline
PROMPT="%m – %*$prompt_newline%n:%~:%# "