Hi Gunther
i have watched several times the holygrail day to night LR 4 video and i have noticed that in that shooting your interval is set from 15 seconds up to 21 seconds
how to you do that 

so far i have been able to set only a constant interval lets say 4 seconds and 3 seconds in between or so 7 seconds for all the shooting programmed

thank you

You can use the LRTimelapse Pro Timer Free to do interval ramping: https://lrtimelapse.com/lrtimelapse-pro-timer-free/