I have heard the line at opening has been long at opening due to people lining up to get the limited Haunted Mansion Tiki Mug. After they buy the mug, then they go inside for the drink. But I've also heard that today was the last day for the Grog Grotto selling the mugs - so lines should go back to normal. The bar is small, so it doesn't take much to fill it up. But if you go at opening without any special things going on, you should be able to get in.