Every comma in a castsequence, except a comma right after an actual spell, is a keyclick where nothing happens.

A few examples...

/castsequence Fireball, Fireball, Fireball
These comma's are not delay's because they follow right after an actual spell.

/castsequence Fireball,,Fireball,,Fireball
The second comma after each fireball is a keypress where nothing happens.

/castsequence ,,,Fireball
These three comma's are keypresses where nothing happens.

/castsequence Fireball,,,
The first is not a delay, because it follows a spell the last two are.

/castsequence [target=party1target] Moonfire,,,,
/castsequence [target=party1] ,,,Lifebloom
This is a spell, followed by three pauses, and three pauses followed by a spell.
Because they never try to cast a spell at the same time, they will not conflict.

Hope that helps some.