Hello Ray, " The only reason for time is so that everything doesn't happen at once." This is a quotation by Albert Einstein not Stephen Hawking. It means the dimension of time is important for things to exist ,if time didn't exist things would happen with no time intervening or wouldn't happen at all.

更正一下，最后一个单词写错了，应该是 once 这句话的意思是：时间存在的唯一价值是用于证明任何事物都不曾存在过。——霍金的《时间简史》