Is a spell's duration tied to its effect, or the time experienced by its caster?
Alternative wording: With regard's to time dilation effects being in play, does a spell's effect last for its designated period from it's own perspective or from it's caster's point of view?
Consider Time Stop and summoning an ally during this spell. Does that ally's duration start counting once Time Stop's effect ends? Or does it start counting down the moment it is summoned, minus any "extra rounds" you used within the effect of Time Stop?
With regards to Harrowed Home (emphasis mine):
As long as you are not in your harrowed home, time ceases to pass for anything and anyone still in your pocket dimension; creatures cannot move, objects do not decay, and everything remains exactly the same as you left it the last time you visited the plane. Time continues as normal whenever you are inside your harrowed home.
Were you to leave a summoned ally inside, would they expire counting on your rounds outside the realm or their own rounds, since they are their own creature and have 'rounds remaining' which is essentially "paused" in your absence from that realm.
If they expire after 'existing outside their native realms for X rounds' that would suggest you can cast dozens of summon monsters and direct them inside the portal (costing you a single round of their existence) where at a later date you can create a new portal and have the dozens (probably more) of summoned creatures pour out of the portal and do battle for you.