This temporary rule challenge is pretty self-explanatory. The smallest subdivision you are allowed to play is eighth notes. This proves especially challenging when soloing. You can do it, but it may cause you some issues. How rhythmically aware are we when soloing or even creating riffs? Now is the time to start paying attention! When soloing using just quarter notes or eighth notes, try perhaps to think more like a singer. What would a vocalist do? What would make for a memorable melody line? The song In Your Eyes by Peter Gabriel comes to mind. Rhythmically speaking, with the exception of the pre-chorus, the melody line rarely drops lower than an eighth note. Can you create a melody line as memorable as that one? It’s not easy. But I think it will open up some new ideas and hopefully make your guitar “sing” a little more.
Remember for now, no sixteenths or smaller. Stick to it and really explore. You may get frustrated or bored, but if you can stick to it and get through that point, that’s when the creativity is truly unlocked. Go for it and have fun!