Death Note 23 Day rule?
The rules together means the following.

Assume I am dying of a fatal disease and expected to die in 14 days. If I would write that I would die of sexual exhaustion in 21 days, I would still die of the original disease in 14 days before the book can come into effect assuming the cause of death is reasonable.

If I put that someone will die in 24 days of "insert horrific image here", it will not occur as stated.  When I remember that rule tommorrow and write that you will die of the same thing on that date... well... it will not be fun to be you.  If you want to avoid that after reading the death note, I guess you can kill yourself and the deathnote will not stop you as that is the end of your normal lifespan.  Note: you should have brought a pen so you can edit the entry.  That works.