Must L + C + R speakers be depth-aligned?

I have two high-end L + R in-wall speakers (that I am planning to mount on-wall in a special enclosure, drivers will sit about 5 inches from the wall).

I am considering buying the matched center speaker (not in-wall). The drivers in the center speaker would sit about 24 inches from the wall.

I understand that in an ideal system, the center speaker's drivers would sit further back than the R + L in a constant-radius arc from the listening positing.

How likely is it that I'll be frustrated with the effects of this? I understand the concept of a timing problem but I don't know what it sounds like. Will I experience a narrow soundstage? Can I remedy this with a surround processor (which I don't own yet)?

Any advice would be appreciated. Here are some details in case you were going to ask:

* Room size/configuration: 13' wide, 11' deep
* Listening position is a couch against the back wall
* I don't have rear speakers yet, those will come later
* Speakers are excellent quality but not extreme - Center used price is ~$1800