"the next day" or "next day" [duplicate]

Cambridge Dictionaries Online has provided examples on the word "next".

Why is "the" omitted in

"What do you think you'll be doing this time next year?"

while next day is preceded by "the" in

"We had a dreadful argument, but he phoned me the next day (= the day after) to apologize."

Do we include "the" before "next"?

In the first sentence "next" refers to a specific year. An alternate for the first sentence might be:

"What do you think you'll be doing this time in 2015?"

In the second sentence "the next" refers to "the following." An alternate for the second sentence might be:

"We had a dreadful argument, but he phoned me the following day to apologize."

similar to:

"The train was full, so we boarded the next train."