When all runes are on cooldown, Ovale shows the time it will take for 2 runes to be available. This seems to be correct.
However, whenever the "swipe" is completed, you can't yet use the spell. Instead it goes to a red icon for less than a second and then it becomes available.

You can see the behavior with just an icon containing obliterate and spamming it.

Include(ovale_common)
Include(ovale_trinkets_mop)
Include(ovale_trinkets_wod)
Include(ovale_deathknight_spells)

AddIcon
{
Spell(obliterate)
}

AddIcon
{
Rune()
}