And we all know that special cases trump general rules.
[sblock]1. independence or freedom, as of the will or one's actions: the autonomy of the individual.
2. the condition of being autonomous; self-government, or the right of self-government; independence: The rebels demanded autonomy from Spain.
3. a self-governing community.
Do I need to explain context as well?[/sblock]
Is the simple solution to allow the Schism Mind to act first doing whatever it was planning to do, than D Door as normal as the final action?
Each of these powers provide text that trumps general rules.
And we all know that special cases trump general rules.
1. independence or freedom, as of the will or one's actions: the autonomy of the individual.
2. the condition of being autonomous; self-government, or the right of self-government; independence: The rebels demanded autonomy from Spain.
3. a self-governing community.
Do I need to explain context as well?
Schism works if your allies can act if they travel with you through a D-Door, "its" standard is still viable ("your mind splits into two independent parts. Each part functions in complete autonomy, like two characters in one body").
As to Celerity, or any other Swift / Immediate action, D-Door does not and can not account for those types of new rules. There for its up to DM interpretation based on all the factors, not just the spell that predates the other components.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.