As for the timeframe issue, I see the scenario spanning out like this.
- Character fires lightning
- Lightning is shown to travel upwards for a couple seconds
- Lightning dissipates
As for how to deal with this, we basically treat said lightning bolt as having actual lightning speed, except that the duration in which said bolt of lightning shown traveling on screen is dependant on the distance traveled instead of the duration of the entire scene said "lightning bolt" was shown traveling.