Agreed, under a strength and hypertrophy macrocycle doing anything over 15-20 minutes should be done in it's own workout. First thing in the morning is best. For hardgainers - a warm-up should just break a sweat, 5 minutes or so... then off to the weights.

Personally I have no problem gaining and workout great with a lot of focus after a 15-20 minute warm-up. If I jump in cold - the switch is basically not on. Off days and light days during bulking I will come in and do 30-45 minutes at a 60-70 percent heart rate - ususally while reading a good book (roughly once per week) and make up for it with more calories just to keep the blood flowin'.

During an Endurance or Deffinition Cycle - working cardio into workouts is ideal.