How import or make date & time data ? & How average time data?

First, I want to import or make date & time data.

For example,

2016-01-01 00:00

2016-01-01 00:01

2016-01-01 00:02

          .
          .

2016-01-30 00:00

And want to average this data. (15min unit)

2016-01-01 00:00

2016-01-01 00:15

2016-01-01 00:30

          .
          .

2016-01-30 00:00