You are making a mistake lots of people make – you are trying to think about what your sentence will look like in English. You might do this with most European languages, but you definitively can't do this with Asian languages.
So as you said, your first sentence is correct:
Basically, all you did in your second sentence was indicate that you are talking about this Friday (the Friday of this current week). This is all about it, your sentence is, of course, correct:
Japanese is like lego, you basically you do: (something + particle)^n + verb.
This is not really true of course since you can have several verbs in a sentence, but basically this is like lego so:
金曜日に => 今週の金曜日に
Since you kept your sentence structure, you shouldn't ask yourself if your sentence is still correct or not. Also, these sentences are also correct:
I just swapped 2 lego, that's all, so my grammar is still correct.