The visit has to be completed before you will be upgraded to Gold. You will be able to use your status for your next stay.
Officially your spring 2008 stay would not be added to this year's stay, so you could not get those 15 nights for Platinum. Loews stays have to be within a calendar year - January 1 to December 31. Conseqently, you would accumulate 5 nights for 2007 keeping you at blue. On January first, the slate supposedly clears and you start over again accumulating stays. So your week stay, at 7 nights would bring you to Gold for your next reservation.
Now, you noticed I said "officially" and supposedly. This is because these are the official rules. However, there have been many reports stating that people were surprised when they got their card in the mail because their stays were accumulating retroactively.
12. LoewsFirst Gold membership requires three (3) qualifying stays or six (6) cumulative nights (associated with a qualifying stay or stays), in a single Loews Hotel or any combination of Loews Hotels, in a calendar year. LoewsFirst Platinum membership requires ten (10) qualifying stays or fifteen (15) nights (associated with a qualifying stay) in a single Loews Hotel or any combination of Loews Hotels, in a calendar year. A calendar year is defined as January 1 through December 31. Retaining membership in LoewsFirst Gold or LoewsFirst Platinum requires meeting the respective criteria for LoewsFirst Gold or LoewsFirst Platinum each calendar year. LoewsFirst members who were LoewsFirst Gold or LoewsFirst Platinum members prior to June 1, 2003 will retain that status through December 31, 2004, unless a higher status is achieved based on the above stated criteria during the calendar year 2003 or the calendar year 2004. LoewsFirst Blue members and new members will become LoewsFirst Gold or LoewsFirst Platinum members when they meet the above stated criteria. Once a Member attains a tier level, this level will remain in effect through the end of the subsequent calendar year. Post-enrollment stays recorded beginning January 1, 2004 are eligible toward tier-level qualification for the calendar year 2005. Thereafter, Members must requalify each year for the following year's membership.