From concert organizers Live Nation:

LOS ANGELES, CA (April 11, 2011) Due to the Los Angeles Kings' first round NHL Stanley Cup Playoff series versus the San Jose Sharks, in which Game 3 is scheduled at STAPLES Center on April 21st, the Lil Wayne concert has moved to:

Friday, April 22nd at STAPLES Center. All tickets for the originally scheduled Thursday, April 21st date will be honored at the Friday, April 22nd show. Tickets for the rescheduled event are also on sale now. For fans that need them, refunds are available at point of purchase.

LA Weekly