Short of creating a new program to specify new times per frequencies, the easiest way to affect the time is to use the Dwell Multiplier setting on the Programs tab.
It defaults to 1. If you change this value, all times will be multiplied by this value and change all times accordingly.
So if you wanted every frequency to run for 1/2 the time, a dwell multiplier of 0.5 would be used.
If you wanted to turn all 3 minute frequencies into 5 minute frequencies, a dwell multiplier of 1.66667 would be used. Note that those frequencies that are not using the default dwell of 180 seconds (3 minutes) would be adjusted accordingly.
Now with all that said, this is for applying frequencies. I should also state you will want to be careful about making things too short or too long, as it could significantly alter efficacy rates depending on the mode you use to apply.
I just re-read your question and noted you stated scan run times. The scan times can not be altered. Each frequency is ran for one pulse sample by default, so a scan will take nearly as many seconds as frequencies being scanned as the average heart rate is about 60.
Take for instance the default scan range of 76,000 to 152,000 Hz. This is a range that is 76,000 frequencies in range, but we are scanning using a step size of 20, so in the end we are going to scan 3,800 frequencies (76,000/20).
At one second per frequency to scan, you arrive at 63 minutes (3800/60).
If you increase the samples/step from 1 to say 2, then you will scan each twice, doubling the time.
The only way to shorten a scan time is to scan less frequencies, which means your scan resolution will be less ideal.
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