The consensus is "whatever you can enforce". Which pretty muchs means nothing, because what it comes down to is gambling on whether the other guy will throw away his set to war you if you retal more than once, or whether you even want to risk that to begin with.

I would say most of the the server accept a retal window that lasts the entire reset. The ones that don't will war over it.

Spy ops are pretty broken on solo servers, by the way. People can and will steal 30 turns of tech from you daily (GDI doesn't protect this spy op nor Bomb Banks) and there is nothing you can do about it without throwing the reset away - once you break GDI, the bomb structures comes in and you're ruined.