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The Schengen visa clock starts ticking when you physically arrive in Paris and pass through Immigration at the Paris airport. The Schengen Borders Code says this at Article 6(2):
...the date of entry shall be considered as the first day of stay on the territory of the Member States and the date of exit shall be considered as the last day of stay on the territory of the Member States...
The entry date must be on, or after, the first "validity date" as shown on your Schengen "C" visa. You must leave the Schengen area on or before the "valid until" date as shown on the visa.