meanwhile vs. meantime

Factual Questions
1

Aren’t you supposed to use “in the” when you use “meantime” in a sentence?

“John was out working in the yard . In the meantime, his brother was inside fast asleep.”

“John was out working in the yard . Meanwhile, his brother was inside fast asleep.”

“John was out working in the yard . Meantime, his brother was inside fast asleep.”

It sounds so irritating to me when people on TV use “meantime” without first saying “in the”.

Has this usage changed?

2

Obviously, if people are using it this way, yes.

Though the OED also says that “meantime” has been used in this way since 1593:

Shakespeare used it, too: