Bubble (not a west Ham fan are you?) IIRC its the 27 days min, which is usually seen as 15 days in camp and that leaves 12, however its all down to the Eff Cert, the CO signs it and it has to be backed up by proof of MATTs and days done, many have missed out on a day or two, however, if you think you are going to be short you can a pply for an extension into 08. Realistically though, 12 days is 48 TNTs with no weekends, so if you were to do only one weekend a month and 1 TNT a month you would have done 27 days.