"... so I got home from work at 5:15 (if only I could get home that early every day! :)"
The problem with this is that the parenthetical statement is never really closed. The ')' character at the end of the sentence is the "smile" part of the emoticon, and it seems awkward to have it act as the closing parenthesis character as well.
As an alternative, I would suggest the following:
"... so I got home from work at 5:15 (if only I could get home that early every day!) :)"
In this version, the parenthetical statement is closed properly, and the feeling that the author is trying to convey by use of the emoticon still comes across clearly, even though the emoticon is located outside the parenthesis.
