Here is a bit on the euro
All EU Member States are part of Economic and Monetary Union, which means they coordinate their economic policies for the benefit of the EU as a whole. However, not all EU Member States are in the euro area – only those having adopted the euro are members of the euro area.
Of the Member States outside the euro area, Denmark and the United Kingdom have 'opt-outs' from joining the euro. These two countries can join in the future if they so wish.
Sweden is not yet in the euro area, as it has not made the necessary changes to its central bank legislation and it does not meet the convergence criterion related to participation in the Exchange Rate Mechanism (ERM II). However, under the Treaty, Sweden is required to adopt the euro once it fulfils the necessary conditions.
The remaining non-participating Member States acceded to the Union in 2004, 2007 and 2013, after the euro was launched. At the time of their accession, they did not meet the conditions for entry to the euro area, therefore their Treaties of Accession allow them time to make the necessary adjustments – they are Member States with a 'derogation', as is Sweden. These Member States have committed to joining the euro area as soon as they fulfil the entry conditions. When this is the case, the 'derogation' is 'abrogated' by a decision of the Council, and the Member State concerned adopts the euro.
National target dates for adoption of the euro
The Treaty does not specify a particular timetable for joining the euro area, but leaves it to Member States to develop their own strategies for meeting the conditiosn for euro adoption. Seven of the 13 Member States who joined the EU since 2004 have already joined the euro area, most recently Lithuania on 1 January 2015.
You could take 10 years to join.
You don't have to join day 1 but it seems you have to accept the euro to join now.