A near 90,000 crowd is expected at Wembley for Man City vs Man United despite more national train strikes leaving tens of thousands of fans having to make alternative plans to travel to London.
Pep Guardiola's City, who have already won the Premier League and face Inter Milan in the Champions League final on 10 June, need a victory to stay on course for a remarkable Treble.
But United, who have already defeated City this season, are looking to follow up their Carabao Cup triumph in February by completing a domestic cup double.
"We want to win a cup, it is not about stopping them," said United's Dutch boss Erik ten Hag.
"We have a great opportunity. Wembley is probably the best stadium in the world and to be there in the cup final is really exciting."
Guardiola said he will play second-choice keeper Stefan Ortega, who has started all five FA Cup games this season, over first-choice Ederson.
It is the first time in 12 years the FA Cup final has kicked-off at 15:00 BST – the previous occasion being Manchester City's 1-0 win over Stoke City in 2011.
Last season's final between Liverpool and Chelsea started at 16:45.
London's Metropolitan Police has categorised the derby match as high risk and objected to a later kick-off time on security grounds.
It is also the first time the FA Cup final between Man City vs Man United, traditionally played in May, has taken place in June, as a result of fixture congestion caused by the World Cup in Qatar last November and December.
The showpiece is being played 70 days before the start of the 2023-24 Premier League season on Saturday, 12 August.
Rival fans heading to Wembley for one of the most cherished dates in the domestic football calendar are being urged to use separate routes and motorway service stations to help minimise disruption.
Major congestion is feared on a day when another train strike is planned.
Rail operator Avanti West Coast is operating a reduced timetable on Friday and no services will run on Saturday because of the industrial action by drivers.
Transport for Greater Manchester (TfGM) has advised City supporters to travel via the M62 and M1; M6 and M1; or M6, M6 Toll and M1.
United fans are urged to travel on the M6, M42 and M40, which is a near-identical distance of about 200 miles (320 km).
City fans are asked to use Lymm, Sandbach, Stafford, Norton Canes, Corley, Rugby, Watford Gap, Northampton, Newport Pagnell, Toddington and London Gateway service stations.
The services suggested for United supporters are Knutsford, Keele, Hilton Park, Warwick, Cherwell Valley, Oxford and Beaconsfield.
United's France forward Anthony Martial will miss the final because of a hamstring injury, while Antony is a doubt as United look to win the FA Cup for the first time since 2016.
The Brazil winger was carried off on a stretcher in the 4-1 win over Chelsea on 25 May.
Asked whether Antony will be available, Ten Hag said: "Unlikely, still a chance but it's a really small chance."
The big news from the City camp is that Ortega will start in place of Brazil keeper Ederson.
Guardiola said he had no fresh injuries and that Jack Grealish, who has not featured since 17 May, and Kevin de Bruyne, who missed the defeat by Brentford last Sunday, have trained.
City are looking to match United's 1998-99 feat when Sir Alex Ferguson's side won the Premier League, FA Cup and Champions League in the same season.
Guardiola's side could win a Premier League and FA Cup double for the second time in their history, after 2018-19.
"We are in the final of FA Cup and it is a pleasure to be here," said the City boss.
"Finals are about how you play in the moment, not what you've done in the past, but how you do individually as a team.
"The final is special. Manchester United are a different team to what we faced at the start of the season. They have improved and so has their quality."
City have reached the final without conceding a goal. They have scored 17 times in five matches.
Erling Haaland has scored 52 league and cup goals for City since arriving from Borussia Dortmund 12 months ago.
Haaland says a historic treble in his first season with Manchester City would be his "biggest dream".
"It would be unreal to make this history," the Norway forward told BBC Sport. "This is why they bought me of course, to get this, we don't have to hide that."
United are contesting their 21st FA Cup final, the joint-most of any side in the history of the competition along with Arsenal.
As well as winning the Carabao Cup, the 12-time FA Cup winners have secured Champions League football next season after finishing third in the Premier League, 14 points behind City.
It all points to a season of progress for Ten Hag and his players whatever the outcome at Wembley.
"I think it is very good when you see where we came from and you see the development and the progress of the team in a tough league," said the United boss.
"When you are third and winning the League Cup and in the final of FA Cup, you can be happy with the season. But I know in summer we start again from zero."
United's path to the final has included wins over four Premier League rivals – Everton, West Ham, Fulham and Brighton.