When does voting take place once an initiative is qualified for ballot?

Legal Regime governing Referenda (Law no. 15-A/98 of 3 April 1998, last amended by Organic Law no. 3/2017 of 18 July 2017)

Article 35: Calling

1 – The act of calling a referendum shall take the form of a decree, which shall not require ministerial counter-signature.

2 – The decree shall include the questions formulated in the draft, the electoral universe that is to be consulted and the date on which the referendum is to be held, which shall be between the fortieth and one-hundred-and-eightieth days counting from publication of the decree, except if the electoral universe encompasses citizens who are resident abroad, in which circumstance the referendum shall be held between the fifty-fifth and one-hundred-and-eightieth days.

Between 40 and 180 days after the publication of the decree calling for referendum.