"We only have twelve seconds." Sounds more natural.
Sounds like spy talks.
or bomb squad, basketball, american football..... or Macgyver
"We have just twelve seconds" is the same
We only have 12 seconds sounds better
By the time you have decided which sounds better... Boom but McGayver
Sounds like she says "sekunttia" :(
That's what it's supposed to sound like. Although Finnish orthography is phonetically consistent for the most part, this is an example of one of the rare inconsistencies.