All solvents must have evaporated from the print before you laminate it.
It may seem the case after 6 hours or so, but they recommend about 24 or 48 hours.
It may seem dry, but the solvents were probably still evaporating, kind of like when you buy a new car - the new car smell is considered to be chemicals still leaking out for many months after manufacture.
Some of my laminated prints are very slightly brittle. They just don't seem to have a nice flexibility about them. It is very slight, but I feel there may be something I am doing wrong?