How Doom Flame spell works?

When some enemy is attacking alliance, they can cast on him the Doom Flame spell which reads:

Death from above. Depending on Spell Charge 5%-20% of all stationary enemy troops in a 3x3 tile area will be killed outright. A maximum of 50000 to 200000 troops can be killed in total. Spell point: 600

It's mentioned that enemy troops (I assume that includes troops in the castle and their reinforcement) will be killed outright, however when spell is casted, there is a countdown of 2h. What does it mean? Does it mean the troops were killed instantly, or not?

If not, or only partial were killed, should Doom Flame spell be used along with the Teleport Freeze to maximalize its effect?

According to @hubbabubbab comment on reddit, the troops will die only at the end of the timer, so if the person teleports out before the timer, it doesn't have any effect.

The troops die at the end of the timer, Most people will work with other alliances so you can teleport block someone whilst they're doom flamed. If the person teleports out before the doom flame timer finishes it doesn't have any effect.

The spell itself is cast only when the timer runs out. These two hours are given for target to react and to casting ally to charge the spell(all ally members can click dragon altar and “charge”, these charges make the difference from 5 to 20% the spell can kill).

However what troops are killed is still a question. Usually, spells are canceled or targets tp away or remove troops from the target zone... I have seen only one hit when we got a report of 16k killed, but still, there are more questions than answers. We know for sure that enemy castle had a reinforcement, the target castle power reduced after spell charged, but the reinforcing castle's power did not change... and of course, enemies didn’t share all the info needed to get how it works with us.