Are you checking with a manual gauge or the electric OEM gauge. If manual gauge it may take a short time longer if you line is very small. The line that I installed the last time had a smaller inside diameter than the old line I replaced and it took longer for the gauge to read pressure and to build up.
You more than likely have pressure to the bottom end right away. It will take slightly longer to get to the top and to the gauge. If your lifters aren't rattling I wouldn't worry about it.