会议被推迟到明天早上10点开始。
至于你的补充，回答如下：先来看下牛津高阶词典中对Delay的释义：
delay
v
[I, In/pr, Tn] (cause sb to) be slow or late 使（某人）慢或迟到; 耽搁; 延误: Don't delay! Book your holiday today! 别拖延! 今天就定下你休假的日子! * She delayed (for) two hours and missed the train. 她耽搁两个小时, 把火车误了. * I was delayed by the traffic. 因交通阻塞, 我迟到了.
[Tn, Tg] put (sth) off until later; postpone 推迟（某事）; 延期: We must delay our journey until the weather improves. 我们必须把旅行推迟, 等天气好转再说. * Why have they delayed opening the school? 他们为什麽延期开学?
你所提问的句子中delay是被动态，所以就是及物动词，因此释义可参照以上第二条。
再者，如果会议是一直开到明早十点的话，那这个句子就不应该用delay，而是应该用last，表示持续动作：The meeting will be lasted till ten o'clock tomorrow morning。