@$abZ:
http://www.onemanga.com/One_Piece/561/14/
The public are like "the execution is starting already? But it's nowhere near the scheduled time" - and straight after Sengoku orders to cut the link because he doesn't want to lose the "trust of the people". Basically meaning that the WG gave the world a time on when Ace will be executed, and don't want to go against their word while the public are watching. That's why Buggy's brilliant plan to keep the cameras rolling is preventing them from be-heading Ace.
Do you really think thats why Buggy did that?