I am a compulsive candler. From day 7-18 I am candling pretty much every day. I just have to be reassured they are still alive. Sometimes I even take a sneak peak before day 7.
You can tell something at 3 days? I can't tell anything at 3 days. I can tell most by 5 days. Maybe because my eggs are light brown.As am I check at 3 days then 7 and every day after.