How to discretize value like EDF ( or other electricity companie )
Energy meters measure energy in kilowatt-hours (kWh). They do not measure power.
The energy meter will count the number of kWh used in the measuring period. This could be 15 minutes, 30 minutes or one hour.
Usually the kWh count is a total count. That means that energy used for an period is given by \$ energy = reading_{end} - reading_{start}\$.
If you only have a power meter then you have to assume the power remains constant for the time period and just multiply kW &times; hours.




Figure 1. A typical energy meter reading graph.


  When I say i have use X Watt of power at 6:00 AM ... I have to use the value between 5 AM and 6 AM or value between 6 AM and 7 AM?


Again, you need to measure energy, not power. The reading will be taken at the end of the measuring period. Now it is up to you how to present this. Think of how you will present the daily readings. You want all the hourly readings for yesterday so you can do:

Period starting    Energy (kWh)
00:00              00207
01:00              00302
...
23:00              00509


Or you could do period ending but then you end with a time 24:00 which does not exist. I think "period starting" is better.


  Can you provide a RFC / ISO or other Scientific paper on the subject?


No. Why would you need one?


  This equipement return a value already discritised at 10 minutes ... but internaly he work lot faster thant every 10 minutes ... So how he discritise the value internaly? 




Figure 2. An old-fashioned energymeter just counts up continuously using a spinning disk. A modern digital meter will integrate power by time to count the energy used.


  The point a 00:10 on my csv is the value from 00:00 to 00:10 or value from 00:10 to 00:20? I want a official document about this, i didn't think every constructor choice by flipping a coin.


The answer to those questions will be in the energy meter and datalogger manuals. You may need to check with whoever configured them during installation.