I don't know what are the factors, but I can guarantee that the durations varies a lot and is not fixed, as tibiawiki claims to be.
First I tested it by throwing 8 magic walls / Wild Growths in a row, 2 seconds between each rune.
- Expectation: They would disappear in same order as I threw them, and with 2 seconds delay.
- Reality: They started disappearing in a random way with random delays, not necessarily in same order as I casted.
So, after that I decided to TIME 10 runes, here are my results:
MAGIC WALL:
- 20 Seconds
- 18 Seconds
- 24 Seconds
- 15 Seconds
- 22 Seconds
- 26 Seconds
- 23 Seconds
- 20 Seconds
- 25 Seconds
- 22 Seconds
MIN: 15 sec
MAX: 26 sec
AVERAGE: 21,5 Sec
WILD GROWTH:
- 47 Seconds
- 50 Seconds
- 37 Seconds
- 34 Seconds
- 52 Seconds
- 35 Seconds
- 36 Seconds
- 50 Seconds
- 37 Seconds
- 44 Seconds
MIN: 34 sec
MAX: 52 sec
AVERAGE: 42,2 Sec