Factbox: Europe votes - Timeline to handover

By Alastair Macdonald

BRUSSELS (Reuters) - EU citizens will elect a new European Parliament this week, the first step in a process that will change the leadership of major European Union institutions later this year.

Here is a timeline:

May 23 - British and Dutch voters are first of 427 million Europeans to cast ballots. Britons should not have been voting at all but must since Brexit is delayed. No British exit polls are expected to be published when polls close at 10 p.m. (2100 GMT). Dutch TV will run an exit poll when voting ends there at 9 p.m. (1900 GMT). Results will be announced on Sunday evening.

May 24 - Irish and Czech voters follow suit on Friday.

May 25 - Czechs keep voting, while the Slovaks, Latvians and Maltese also cast their ballots on Saturday.

May 26 - Rest of the 28 states vote, using various types of proportional representation that ensure a multitude of parties get seats. From 1600 GMT, exit poll from Germany, the biggest country, will offer clues. France, the second biggest, and Spain follow at 1800 GMT. The European Parliament will publish a first projection for all seats based on exit polls in 12 countries. It will update this, adding Poland and three other countries, after 1900 GMT and again once the final vote is cast, in Italy, at 2100 GMT. An authoritative, though still provisional projection, using partial results, is due from Parliament at about 2215 GMT.

May 27 - Parties will start working out how best to play the hands voters have dealt them in forming official groups in the chamber and broader coalitions, seeking a majority. Leaders of four main pro-EU groups meet in the evening to agree a push to have one of their own appointed EU chief executive.

May 28 - Parliament's Conference of Presidents -- leaders of party groups -- to meet in the morning. Expected to endorse call for national leaders to nominate lawmaker to run EU Commission.

From 1500 GMT, 28 EU national leaders meet over dinner in Brussels to debate their next move -- giving their chairman, Donald Tusk, a mandate to negotiate the bloc's top jobs.

June - Parliamentary groups will negotiate among themselves and with Tusk, seeking to defend the legislature's demand that government chiefs nominate a party candidate to succeed Jean-Claude Juncker as president of the executive European Commission. Many national leaders are resisting that idea.

June 20-21 - Leaders aim to agree on Juncker's successor and that of European Central Bank President Mario Draghi. They may also agree who will succeed Tusk himself as president of the European Council and EU foreign policy chief Federica Mogherini.

July 1 - Theoretically, Britain could leave the EU on this date if the UK Parliament agrees a Brexit deal at the fourth attempt. If it did, British MEPs would not take up their seats. However, this appears extremely unlikely at the moment.

July 2-4 - New Parliament convenes in Strasbourg. It should choose its own president to succeed Antonio Tajani on July 3 -- another job in the mix for the bargaining over key EU posts.

July 16-18 - Parliament sits again in Strasbourg. This is the earliest it could endorse a new Commission president.

July-August - If a Commission president is agreed, he or she would then build an executive team, taking one commissioner from each member state and giving them portfolios. If there is no deal on a successor, then more summits may be needed. In 2014, Tusk and Mogherini were nominated at a summit in late August.

September - New commissioners face hearings in Parliament. Some, notably those nominated by eurosceptic governments in the likes of Italy, Hungary or Poland, could hit resistance but MEPs can only block the Commission as a whole, not individuals.

Oct. 22-24 - Parliament due to vote in Strasbourg to confirm the new Commission as whole. It can withhold its endorsement.

Oct. 31 - Britain is due to leave, deal or no deal -- though a further delay to Brexit is also possible.

Nov. 1 - The Commission is due to take office. If it has not been confirmed by Parliament, Juncker's team would carry on. Draghi's successor is due to take over the ECB in Frankfurt.

Dec. 1 - Tusk's successor due to take office at the Council.

(Reporting by Alastair Macdonald; Editing by Andrew Cawthorne and Catherine Evans)