There's been a bit of confusion over whether Mitcham Eastfields station would open on Sunday or Monday. In particular, the National Rail Enquiries site had trains in the timetable for Sunday, and explicitly gave that date in its notes. That's now been fixed. The first train to call at the station appears to be the Southern service from Epsom to Victoria at 5:49am. If you want to be on it, First Capital Connect run all night to East Croydon, where you can catch an early tram to Mitcham Junction, one stop before Eastfields on the Southern service. The National Rail page notes the footbridge will be available "from Summer 2008", implying it won't be ready for this weekend. Photo taken two weeks ago. Hopefully it's finished by now.
Update: The opening's been postponed again. See the comments.
Update 2: Opening at 4pm today. The first train to call will be the Epsom-Victoria at 16:10