Viper Channel 4&5 Outputs

I have a 791XV and am using the channel 4 & 5 outputs for windows up and down.  Right now I have these set to validity outputs so I have to hold the button down until the windows are all the way up or down.  I'd like to have it do it automatically and could use the 30 second mode to do it.  The windows have limit switches so they'll stop when at the top or bottom even if the output is still there. But I was wondering if there is a way to set these to output for less than 30 secs (like maybe about 8 or 9) by using a Bitwriter or something.  It didn't say that was an option in the manual but I thought I remember that from some older models.  Or are there any other suggestions for a simple way to do it?

Thanks,

~John