Decoction and the main mash

Hi,

I'm currently reading the excellent book "Brewing better beer" by Gordon Strong but I have a question about a thing he mentions when he covers decoction and I was wondering if anyone that has experience with the process can answer it(I've only ever used single-rest infusion but I'd like to give decoction a try to make a Dunkel).

He says that when you take part of the mash to bring it to a boil, you should increase the temperature slowly and that this is what makes decoction such a long process. I was wondering how this long time affects the main mash. This will make for a longer mashing time for the part that remains in the main mash.

Any thoughts on this would be appreciated.

Thanks
-M