Calculate average by date with unusual date column format

[my8950]

I am trying to make a worksheet that will calculate the averages or a sample taken every 5 minutes constantly. The date column increments in minutes, but comes out with the date attached as well.
A sample is below, this is only a few lines:2019-05-21T00:03:40
2019-05-21T08:28:40
2019-05-21T15:33:40

Is there a way I can specify to only take the date? My goal is to take all the sample per day to create one average.
I am using a formula to calculate the averages - =AVERAGEIF($A1:$A10000,G1,$C1).

The overall output file may contain 14 days or so of data, I'm only after making an average of each days information.
This is just a small part of a larger "idea" I have to my semester project.

Thank you...

 

[DSCfromCFA]

G'day my8950,

You can use the LEFT function to either extract the date component into a helper column
=LEFT(A1,10) (If your longform date is in A1)

or

directly into a formula (providing the formula recognises this as a date) such as
=MONTH(LEFT(A1,10)) OR
=IF(DAY(LEFT(A1,10))=21, etc etc etc.

cheers

shane

 

[my8950]

Thanks for that information...I will give it a try when I am back working on the macro, should be interesting!

 

[my8950]

Decent, it will work to cut out the time portion of my date line. Thanks!

 

[DSCfromCFA]

You're welcome, and thanks for letting me know.

Cheers

shane