Convert 15 minute data to 30 minute data

[Challis]

Hi,
I am looking to convert 15 minute data to 30minute data as below (for 1000s of rows):
[TABLE="width: 713"]
<colgroup><col><col span="3"></colgroup><tbody>[TR]
[TD="align: right"]1/01/2019 8:15[/TD]
[TD="align: right"]1801.669[/TD]
[TD="align: right"]1/01/2019 8:30[/TD]
[TD="align: right"]3602.79[/TD]
[/TR]
[TR]
[TD="align: right"]1/01/2019 8:30[/TD]
[TD="align: right"]1801.121[/TD]
[TD="align: right"]1/01/2019 9:00[/TD]
[TD="align: right"]3606.543[/TD]
[/TR]
[TR]
[TD="align: right"]1/01/2019 8:45[/TD]
[TD="align: right"]1803.261[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]1/01/2019 9:00[/TD]
[TD="align: right"]1803.282[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

What is the easiest way to do this?

 

[steve the fish]

You could use a SUMIFS

=SUMIFS(B:B,A:A,"<="&C1,A:A,">"&C1-1/48)