What is the deadline for collecting required number of signatures?

Law on National Referendums, Legislative Initiatives and European Citizens’ Initiative (last amended in 2012)

Article 7 (1) The Central Election Commission shall set a term of 30 days during which the signature sheets for voters to sign shall be available at the places designated by city or municipality councils. The term should include successive days, excluding days when the elections of the Saeima, the European Parliament, city or municipality councils or national referendums take place and when the collection of signatures for petitioning a national referendum is not permitted.

30 days