The important dimension is how far away is each L&R main speaker?
If you were to take a piece of string and measure from the front face of the speaker (close to tweeter) to your ears, the distance should be the same for all speakers (L, R, Center, LS, RS).
For those speakers that are closer you want to ADD some delay. How much? It depends on how your receiver/prepro measures this (feet or ms). Typically you use 1 foot or 1ms of delay for every foot closer a speaker is.
So, if your mains are 10 feet from you, you would add a delay of 2 to the center (10-8=2) and a delay of 1 to the surrounds (10-9=1).