There are a couple of deadlines here.
1.) the Monday of the 10th week of the season - any salary increase for that season after that date is treated as a signing bonus for salary cap purposes and will be prorated over the new length of the contract.
Examples.
Raise Tedy's salary by 2 million dollars in Week 3. That salary increase hits only the 2006 cap. Raise Tedy's 2006 salary in Week 13. That salary increase is prorated over 2 years (the life of the contract.
2.) the end of the regular season. Any deal done after then will not affect the 2006 cap year.