i've read from wiki that payment is to last n shares where n is the smaller of :
1. 3x the work needed to generate a block;
2. some 8640 shares (3 days)??

which ever is smaller......

so in practice each share can only live for something like 1.5 days only right can someone explain how situation 1 above works??? how did the system determins the average works needed to generate 3 blocks??? actual or predicted???