There is time, dont get me wrong, but thats based on a cool calm and collected person who knows exactly what they are doing. If you go over your steps, its without emotion involved and retrospective. In realtime its a hysterical parent and grandparent who just happen across their child, choose not to perform first aid or CPR, determine he is dead, argue/debate about what they should do and then come up with a plan and then carry it out, then get their story straight and convince a little girl of the story. Then convincingly for 7 years cover it up. its a lot to process, especially if they are basing this on bindis and shoes from the photo as proof that she is inconsistent. Im not saying this didn't happen, but OMG the luck, audacity and brazenness needed to do it successfully is insane.
Also she is the one dictating the time frame. She called the cops. She could have waited, given herself more time..