Oh sweeps. The time of year when the weather is nice but the TV shows are at their prime. NBC is pulling out all the stops by extending its top shows by 10 minutes - all in HD too. Most DVRs should be able to handle this if the guide is downloaded properly. It would be worth your time though to set the DVR to extend 10 minutes past the end of the show just in case though.
NBC is using this technique on Will and Grace, My Name is Earl, and The Office's May 11th showing. TV Squad also pointed out that a long time HD classic, ER, is going to be 10 minutes shorter. (does anyone still watch ER though)