To put this into some sort of perspective.
The group aircraft's engine holds 8 quarts of oil, thats 2 gallons. Last weekend the temperature was 2deg C. So imagine a domestic bucket full of oil just above freezing point - I certainly wouldn't want to put my hand in it. It would be painfully cold and stiff like treacle.
The POH recommends keeping the revs below 1400 until the temperature reaches 40deg C, which is the maximum temperature recorded in the UK last summer.
So what we are asking the engine to do is to take a bucket of treacle from just above freezing to midsummer temperature - its not surprising that it can take 10 minutes.
But its definately worth taking the time to do it.