Last minute helper is that person who shows up AFTER everything else is done and offers to do something AFTER everything is already finished.

Last minute helper指所有事情都完成以后才出现，或者别人把所有事情都做完后才提出帮忙的人，我们称为“事后帮手”。

For example:

Joe showed up when we got all the dishes ready. He offered to set the table, but Mary already did it. He is definitely a last minute helper, you cannot count on him.

乔来的时候，我们已经做好菜了。他要求摆置餐桌，可是玛丽早就摆好了。他绝对是个事后帮手，一点都指靠不上。