Do we already have the capability to destroy or deflect incoming asteroids, say, on a week's notice?

Depends on the m and material of a meteorite. We get bombarded by them day and night, thousands a day. They usually break up or totally disappear as gas, entering the atmosphere. We could see a real dangerous one (extra large) month ahead. It would be very complicated to calculate, if it would just fly by or really hit the earth head on, since their are so much gravity deflections on its way towards earth. The chance of a rock just the right size for our current technology to deflect, hitting the earth is almost zero, but I wouldn't man a deflection rocket with NASA pilots.