hi, all,
i just purchased an intervalometer, a viltrox from the East, hong kong i think, and am wondering about using camera shutter speed of 40 secs for night time and moving traffic. i set interval for 55 sec but i'm not getting any previews. is this incorrect. i'm using a canon 7d and it writes to the card before next exposure, should i just turn off previews or extend interval time? the card is getting the images on a test, but i'm worried about the buffer being over whelmed.
any suggestions would be appreciated, thank you.

Don't set the exposure time on the intervalomet, set as short as possible there and set it in the camera instead. I don't think 40sec is a good choice for time lapse, this will usually be too long. Just go for 15 or 20 secs max, set this time in the camera and make sure the the intervalometer only generates a very short impulse to trigger the camera.
Read this article too: http://lrtimelapse.com/news/intervalometer-hack/

thank you. should i set an interval time on my intervalometer for about 28 secs if i use 25" for  shutter speed on camera or leave interval time at 0? the manual says to keep at 0.
Eric