After the Saturday Whistler disaster, we vowed to never ski a weekend again. So the trip would definitely be weekday skiing.
Saturday is my rest day at whistler, but you can navigate around to beat the crowds. Get to harmony and symphony as soon as they open. Get two quick rips in on Symphony and head back down to Emerald Express as Symphony will plug up in a hurry. Hang on Emerald or Big Red for a couple runs, then up the peak express for a Peak to Creek run around 10:30-11:00. Grab a snack and drink below, hop on the creekside gondola and back up Red. Go back to harmony while people go in for lunch.
This pattern works pretty well any day of the week, but whistler is best Monday to Thursday. There is very little wait and huge terrain to explore.