>So if you have this:
>"At home."
>
>"At" = preposition;
>"home" = noun.
>"At home." = prepositional phrase.

Which you rarely hear. The common one is "I'm home".

When was the last time you heard something announced to "start on friday"? Nowadays, it all "starts friday". Now if your friday won't start, just use any of those things which are guaranteed to start it :).