Information structure, again. It all depends on where you put the focus of the utterance.
Am Freitagabend spiele ich gern Gitarre.
Ich spiele gern am Freitagabend Gitarre
These are equally neutral, but can be interpreted as focussing the object Gitarre, especially if you emphasize or contrast it (Gitarre, nicht Bass).
Ich spiele gern Gitarre am Freitag Abend.
Also works fine, but is slightly more marked to focus on the time. (As you can see, focussed parts tend to come last in a sentence.)
Am Freitagabend spiele gern ich Gitarre.
Now, this is heavily marked. It looks, on the first glance, ungrammatical to even native speakers, but it absoluty works in contexts where you focus ich for contrast. In speech, you must (!) also stress the ich. Example context -- imagine A is asking a gig of B's band:
A: Spielt X morgen wieder Gitarre?
B: Nein, am Freitagabend spiele gern ich Gitarre. Er ist am Samstag wieder dran.
In addition, you may exceptionally use the syntax with some poetic license:
Am Freitag spiel' gern ich Gitarre,
und rauch' dazu ne feine Zigarre.
This is without focussing on ich, and just for the sake of the rhyme.