Hi
1. lt_trend is the variable for the last traded price trend line in the chart editor. The time period is as per your chart settings, i.e. last x minutes or last y refreshes and the smoothing parameter.
2.2. (event_start-now_time)/mf_second will give you a countdown in seconds to the scheduled start, the figure turns negative after the time of the scheduled start.
If you reverse that, (now_time-event_start)/mf_second will give you a minus countdown in seconds to the scheduled start, the figure turns positive after the time of the scheduled start.
for example, you could use a condition like this to limit triggering to a delayed start of no more than 20 seconds:
and selections trigger expression (now_time-event_start)/mf_second is less than 20