The wikibase-time-precision-* messages have unclear context and documentation.
"in $1 billion years" can be used in the phrases "$1 billion years *from now*", "*once* in $1 billion years", "in units of $1 billion years", etc. The current documentation doesn't make it clear what is the required sense. The qqq strings must be updated to reflect this.
Furthermore, I suspect that the full stop is not needed in English in "$1. millennium" and "$1. century". If I'm not mistaken, a full stop is needed after numbers in some languages in some cases, but it's not needed in English. I might be wrong in my suspicion, but in any case this must be clarified in qqq.
Finally, the message Wikibase-time-precision-century is extremely unclear. Is "$1s" really a good string for English?
Whiteboard: u=dev c=frontend p=0