The meeting, originally set for July 3, will now occur at the end of July. The move signals that Yahoo! chief executive officer Jerry Yang is under pressure to prove he can win investors back after rejecting Microsoft's offer.
Last week, Icahn said that he would seek control of the board if Yahoo! directors failed to agree to a merger with Microsoft. He has plans to put forward his own slate of directors for shareholders to vote on.
Microsoft abandoned its bid for Yahoo! on May 3, three months after its initial advances. Yang had demanded at least $37 a share for the company he co-founded in 1994.
On May 18, Microsoft announced it was pursuing a new deal with Yahoo! that didn't involve a takeover, but said it may reconsider a Yahoo! bid at some point.
Last night, Google co-founder Larry Page attacked Microsoft's plans to takeover part of Yahoo!. He said that a Microsoft acquisition of Yahoo! would harm innovation by giving the combined company too much control over web communications.
He said: "Now, if you put 90% of communications all in one company... that's really a big risk, especially one (Microsoft) that has a history of doing bad stuff.
"If you want to have good products you need to have some degree of openness."
The comments come as Google pursues its own agreement with Yahoo!, which involves selling advertising for some of Yahoo!'s users' internet searches.