AoS Allegiant ability

I am not quite sure what you mean.

Anyway this is how it works:
You always get Lords of Space and Time if you are Seraphon allegiance.
It does not collide with anything in our army. So the answer is probably yes

Edit: corrected autocorrect error

 

Yep, you can always use the lords of space and time allegiance ability (it's not required that you must have a Slann to use it).
A Slann can let you use it twice (if you pick the specific trait for the Slann)

 

Ah ok much more clear now.
Yes you can use both.

 

Yep, those are the ability of the Allegiance. with a Slann, you use Master of Order and Lords of space and time.
Without a Slann, you can only use Lords of Space and Time