Several sites discuss Wheelbarrows at Dawn: The Lost Box of Tolkien Memories but only one seems to have its dates in order (a point I must qualify by saying the writer conceded -- at the time he wrote the announcement -- the book was only partially finished). So, some details were published on ADC Books and Art's site, but they didn't have a date.

They sent a message to TheOneRing.Net but neglected to include a month or year.

By process of elimination, careful deduction, judicious use of a search engine, and the dumb blind luck of finding co-editor Neil Holford's description of the project on his site Tolkien Books, I figured out that the launch will start on Friday, March 26, 2010.

He writes:

The book is based on a box of letters, photographs, cards, paintings, notebooks and other gems that were gathered by Hilary over the course of his long life. The box’s contents have now been made available to tell a tale that begins before Hilary was born in Bloemfontein in 1894, then follows him to Birmingham and Gedling, through his time in the army and onto many years of living and working on his fruit farm in Blackminster, continuing even after his death in 1976.

So, read the whole article on Neil's site and be sure to look at TheOneRing.Net's announcement because they have some details you won't find on the other sites.

It all sounds quite interesting to me. I'll publish more information if/when I get it.