I'd consider upping the dose and grinding a little coarser til you hit the same time, and also pre-infusing at a lower pressure until the first drops form on the bottom of the portafilter. You could also try that independently if you're not doing it already. Good luck!
Also, does it eventually fill the screen and form a single stream? If it does this for like 5-15 seconds and then steadies, that could be totally normal and I wouldn't worry about it if it tastes good.