I agree with that, but I'm thinking in terms of this specific incident.
If we recap, until OP gets that door open he doesn't know what's happened. He doesn't know if Reeva's dead, alive or fell to the floor unconscious. He doesn't know where the bullets have gone inside that toilet or how many may have hit. He has no information to tell the emergency services at that stage. This is why my primary concern would be to get the door open, see where the bullets have gone and and try to stem any immediate bleeding.
This only applies if OP didn't hear Reeva screaming, which is his claim.
If he had heard Reeva screaming, then he'd notice that the screaming had stopped, and would presume he had killed, or at the very least seriously wounded Reeva. In that scenario it wouldn't matter when he made the call.
Completely false to say "Until OP opens the door he doesn't know what's happened." OP claimed he knew with 100% certainty somebody was in the toilet, he shot four times, and then there was no response from the person in the toilet.
And you're saying it's more important that spend 5 minutes dicking around trying to open the toilet door just so he knew if the person he shot would need an ambulance or not?
And there was no urgency to call for help if she was already "seriously wounded" and on the verge of death?
Seriously? Do you really believe this?
The truth is he knew she couldn't be helped. He already knew he blew the brains out the back of her head. That's why he called Stander first and by the time Stipp arrived, neither Stander, Clarice, or OP had called anybody for help.
In fact, the one person who could have helped, Baba, was told everything's ok.
Do you believe the gun shot itself too without OP pulling the trigger?