Among the reasons loading that way can be done safely is because they use proper judgement about letting the proper length of time pass between taking the last shot in the cylinder and the start of the loading process where they start to drop in the fresh powder charges.
What the proper amount of time is to allow for any embers to burn out is a matter of experience.
For instance, whenever there's a misfire with a percussion cap, safety rules would require that a period of time be allowed to pass before the load is considered to no longer be a hang fire. That period of time could be considered to be anywhere from 30 seconds to 1 minute or more. Wait double the amount of time if you feel that's necessary.
Don't take this personally, but even a lot of words cannot make an invalid statement fact.
You are wrong.
The "safe" amount of time may be much longer than you may think it is.
Here is story of an incident I observed. It was at my club range. I was range officer that day.
A member, named "Scotty" went to the firing line to shoot with his single shot pistol. The cap went off but gun did not. Doing as he should, he kept the muzzle down range and waited. He said several times, "I know I loaded it." He stood there for some time repeating that. Then he raised the muzzle pointing up and started back to the loading bench to pull the ball. He still, wisely, kept the muzzle up. He changed his mind and went back to the firing line with the muzzle still pointing in a safe direction. Well, this went on for more than five minutes, maybe ten. Finally convinced he hadn't loaded, he turned to go back to the loading bench, with muzzle still up, when the pistol went off.
No doubt, the cap igniting left a tiny smoldering ember somewhere in the breech area of the pistol and after 5 to 10 minutes it finally ignited.
I was an eye witness, as range officer watching this shooters gun handling very carefully. I know what happened.
It was a valuable experience and lesson.
For me, your 30 second to two minute thing is only a disaster wanting to happen.
Never, ever, never-ever, load directly from a flask.