in the meantime 在…期间,同时； 与此同时,意思是指,在一件事未结束之前,另一件事也发生了.与此同时并不是指特定的一个时间点儿.
例如：You go back to school to learn a new trade and hope you can keep the family together in the meanwhile.
at the same time 往往强调事情同时发生,
例如：I can’t attend to everything at the same time 我不能同时处理每件事