"Get off after two stops!"
Translation:İki durak sonra in!
If you can't say 'X later' instead of 'after X' use the ablative. The sentence Get off two stops later. is also possible then don't use the ablative.
It would be handy if there were something more concrete than trying to reword it in English (surely, the ultimate goal is to think in Turkish).
The plural ending is only used when the plural isn't already implied (in this case, it's implied by "iki").
Also, "sonra" is a postposition, not a preposition. So, it's "iki durak sonra", not "sonra iki duraklar"