8 days in 1 out of 5 sprouted. Is this normal?

devil's advocate on top of other things mentioned -- how old are those seeds? if not at least 1 month beyond harvest, they may not be ready yet. Seeds need a little after harvesting before they are viable and if that is the case could be cause of a low-germination rate. Same with really old seeds... Depth at which you plant is key to how long this takes. So are temperatures of substrate. Get a heat mat and it'll greatly increase consistency of this timeline, too. you want one with a thermostat you can plug into soil, not the free willy kind. Kickin myself for not getting one sooner. Loving the effect it has on a good process. first digit of finger depth... loosely cover and gently tamp.. if you find shells still attached, either tamp down a bit more or bury deeper next time. Find that happy zone of speed and no shell-heads. Keep it simple..

Depends on your germination method. Just planting in the soil no prep work 1 week is not unheard of but given the other one has popped it seems off. I tent to see seeds pop in 1-3 days after soaking them and placing them in the medium. after that I begin to worry a bit. As Organoman said you soil might be a bit to dry and that can kill seeds. or they were bunk seeds. if you got them from weed you bought that might be why.

No, it is not normal.........your "custom breeder" may noy be that reliable, but after looking at your diaries, your soil mix looks very dry, which can be terminal for "popping" seeds. Soil for gemination needs to be kept moist at all times, but not wet, until they emerge and never allowed to dry out.