The command block delay setting would be a setting like how there's the conditional/unconditional button in the GUI of command blocks, and it would allow delays to be put on command blocks. You would type in a number, which would be the delay (in ticks) that the command block would have.
How the delay works would be different depending on the command block type.
Impulse: The delay would make the command block not execute its command until X ticks after it is powered by redstone.
Chain: The delay would make the command block not execute its command until X ticks after the command block behind it executes its command. (So if you have three chain command blocks in a line all with 20 ticks delay then they'd all execute their commands one after the other with a 20-tick gap between each)
Repeat: The delay would make the repeat command block only execute its command once every X ticks, rather than every single tick which is currently the case.
Why should this be added:
Currently the only way to have delays on command block executions is to use repeaters, and that can involve a lot of tedious placing and setting them all to full delay (or using /fill to place them, but even then you still have to make sure they're pointing in the right direction).
With the repeat command block delay, you don't really need some commands to execute every tick, as the thing that I've been finding is that if you have a ton of repeating command blocks executing their commands every tick, it tends to cause lag, thus rendering Minecraft practically unplayable. I tend to create comparator clocks to execute such commands once every half-second or so, which still works for the purposes of my maps but does not create lag.