How to average values measured continuously every 20min for a given amount of days ?

As the title is not very clear, here is a better description of my problem.

I have a set of data that I have obtained by measuring the air temperature (C) in a greenhouse every 20 min, using an electronic data logger. That means that the data logger has recorded automatically the temperature every 20 min for almost 4 months.
I have transferred the data collected by the data logger in the greenhouse on my computer.

Now, I'd like to obtain a graph showing the average diurnal variation of the air temperature for the month of, say, April.
For this, I need to average the temperature values that have been recorded at the same time of the day, for 30 days.
Hereinafter are given the Temperature values for 2 days in february (the 4th and the 5th). The last two numbers are the temperature (in Celsius) whereas the previous number corresponds to the day-mont-year and hour (XX:YY).

What I want is, for every 20 min at the same time of the day. obtain my average temperature value for a whole month.
Once i have this, I'll be able to create a graph with the hours of the day as abscissa (0 to 24) and the temperature as an ordinate.

Thanks in advance for your help !

Date Temperature
04-02-2016 00:00 18
04-02-2016 00:20 17
04-02-2016 00:40 16
04-02-2016 01:00 16
04-02-2016 01:20 15
04-02-2016 01:40 15
04-02-2016 02:00 14
04-02-2016 02:20 14
04-02-2016 02:40 14
04-02-2016 03:00 13
04-02-2016 03:20 14
04-02-2016 03:40 13
04-02-2016 04:00 13
04-02-2016 04:20 13
04-02-2016 04:40 13
04-02-2016 05:00 13
04-02-2016 05:20 13
04-02-2016 05:40 13
04-02-2016 06:00 13
04-02-2016 06:20 13
04-02-2016 06:40 13
04-02-2016 07:00 13
04-02-2016 07:20 14
04-02-2016 07:40 17
04-02-2016 08:00 21
04-02-2016 08:20 24
04-02-2016 08:40 27
04-02-2016 09:00 30
04-02-2016 09:20 32
04-02-2016 09:40 33
04-02-2016 10:00 35
04-02-2016 10:20 37
04-02-2016 10:40 38
04-02-2016 11:00 39
04-02-2016 11:20 40
04-02-2016 11:40 41
04-02-2016 12:00 41
04-02-2016 12:20 43
04-02-2016 12:40 43
04-02-2016 13:00 43
04-02-2016 13:20 43
04-02-2016 13:40 42
04-02-2016 14:00 43
04-02-2016 14:20 42
04-02-2016 14:40 42
04-02-2016 15:00 40
04-02-2016 15:20 40
04-02-2016 15:40 40
04-02-2016 16:00 40
04-02-2016 16:20 39
04-02-2016 16:40 38
04-02-2016 17:00 36
04-02-2016 17:20 34
04-02-2016 17:40 32
04-02-2016 18:00 30
04-02-2016 18:20 27
04-02-2016 18:40 25
04-02-2016 19:00 26
04-02-2016 19:20 26
04-02-2016 19:40 26
04-02-2016 20:00 26
04-02-2016 20:20 26
04-02-2016 20:40 26
04-02-2016 21:00 25
04-02-2016 21:20 25
04-02-2016 21:40 24
04-02-2016 22:00 21
04-02-2016 22:20 20
04-02-2016 22:40 19
04-02-2016 23:00 19
04-02-2016 23:20 21
04-02-2016 23:40 20
05-02-2016 00:00 21
05-02-2016 00:20 22
05-02-2016 00:40 21
05-02-2016 01:00 20
05-02-2016 01:20 20
05-02-2016 01:40 19
05-02-2016 02:00 18
05-02-2016 02:20 20
05-02-2016 02:40 19
05-02-2016 03:00 18
05-02-2016 03:20 17
05-02-2016 03:40 17
05-02-2016 04:00 17
05-02-2016 04:20 17
05-02-2016 04:40 16
05-02-2016 05:00 16
05-02-2016 05:20 15
05-02-2016 05:40 15
05-02-2016 06:00 15
05-02-2016 06:20 14
05-02-2016 06:40 14
05-02-2016 07:00 15
05-02-2016 07:20 15
05-02-2016 07:40 19
05-02-2016 08:00 23
05-02-2016 08:20 26
05-02-2016 08:40 29
05-02-2016 09:00 31
05-02-2016 09:20 33
05-02-2016 09:40 34
05-02-2016 10:00 35
05-02-2016 10:20 36
05-02-2016 10:40 37
05-02-2016 11:00 37
05-02-2016 11:20 38
05-02-2016 11:40 40
05-02-2016 12:00 39
05-02-2016 12:20 40
05-02-2016 12:40 40
05-02-2016 13:00 41
05-02-2016 13:20 41
05-02-2016 13:40 42
05-02-2016 14:00 41
05-02-2016 14:20 42
05-02-2016 14:40 41
05-02-2016 15:00 41
05-02-2016 15:20 39
05-02-2016 15:40 40
05-02-2016 16:00 38
05-02-2016 16:20 36
05-02-2016 16:40 36
05-02-2016 17:00 34
05-02-2016 17:20 32
05-02-2016 17:40 31
05-02-2016 18:00 29
05-02-2016 18:20 28
05-02-2016 18:40 27
05-02-2016 19:00 27
05-02-2016 19:20 27
05-02-2016 19:40 27
05-02-2016 20:00 26
05-02-2016 20:20 26
05-02-2016 20:40 26
05-02-2016 21:00 26
05-02-2016 21:20 25
05-02-2016 21:40 25
05-02-2016 22:00 25
05-02-2016 22:20 24
05-02-2016 22:40 24
05-02-2016 23:00 24
05-02-2016 23:20 24
05-02-2016 23:40 23

Try


F1=0, G1=20, H1=40

in F2 and copy across to H2

=SUMPRODUCT(($C$1:$C$144),--(MINUTE($B$1:$B$144)=F$1),--(INT($A$1:$A$144)>=DATE(2016,2,1)),--(INT($A$1:$A$144)<=DATE(2016,2,29)))/SUMPRODUCT(--(MINUTE($B$1:$B$144)=0),--(INT($A$1:$A$144)>=DATE(2016,2,1)),--(INT($A$1:$A$144)<=DATE(2016,2,29)))

Hi
Try this approach
Assuming real dates in A2:..., and temperatures in B2:...
Use a helper column in C2:...

Formula:

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and copy down
Use in D2 and copy down

Formula:

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Another way ...

=AVERAGE(IF((MONTH($A$2:$A$5000)=MONTH(A2))*(MOD($A$2:$A$5000,1)=MOD(A2,1)),$B$2:$B$5000,""))

Enter with Ctrl+Shift+Enter

Hi guys !

Thank you for your help, all three methods worked quite well !

Have a good day