using intervalometer with long exposure times - what time setting to use?

[Hillbrook]

Hi there, maybe a silly question but does the intervalometer time start at the close of the shutter or the opening of it? In other words if i am shooting a timelapse of the stars, and open the shutter for 13 secs, do i set the intervalometer to go off every say 15 secs (giving camera time to stay open for the 13secs before intervalometer shoots off another shot?) so it would fire again 2 secs after current shot finishes or ??

Hope this makes sense.\

Cheers, Hillbrook

[Walter Schulz]

I don't want to sound rude but why not testing it by yourself?