The quoted rules from the Player’s Handbook description of the Craft skill are near-literally the only rules I can find anywhere that touch upon how long it takes to craft anything non-magical. The only exceptions I can find are the Dungeon Master’s Guide rules for trapmaking, the Dungeon Master’s Guide II rules for item templates, and the Drow of the Underdark rules for poisonmaking.
Rules Compendium doesn’t even bother to repeat the Player’s Handbook rules, and doesn’t touch on the Craft skill at all, which is kind of astonishing. And despite the fact that the errata for both Player’s Handbook and Dungeon Master’s Guide explicitly label the Dungeon Master’s Guide the “primary source” on “special material construction rules,” it doesn’t have any. It only describes what the advantages are for something that was constructed with such materials, nothing about the process of something getting that way. The Rules of the Game articles don’t even cover Craft, which again seems bizarre since it’s a fairly major thing and the rules are really confusing.
Which means literally all we’ve got here is
Find the item’s price. Put the price in silver pieces (1 gp = 10 sp). […] Make an appropriate Craft check representing one week’s work. If the check succeeds, multiply your check result by the DC […] it represents the progress you’ve made this week. Record the result and make a new Craft check for the next week. Each week, you make more progress until your total reaches the price of the item in silver pieces.
No commentary, discussion, or caveats on “the item’s price.” Masterwork is a separate “component,” as are the DMG2 item templates, so we know those are worked out separately. Those also have separate Craft DCs, which special materials do not. And magical crafting, of course, is an entirely different system, and the rules specify that the costs and crafting of the magic part of an item are entirely independent. But nothing says that about special materials, or anything else. Rules-as-written, then, “the item’s price” is just that, whatever the item costs, however it got to cost that much, excepting masterwork, item template, or magic.
Which, yes, means that adamantine full-plate takes about half a year to craft.