Probably something I should have mentioned before is ....try to get your subs so that the Histogram peak is around
1/3 the way from the left (dark point)...when using DPP or PS (or any program that shows the histogram).
If you get less than this the subs are tending to be underexposed. You can go longer and get more data.
If you go more...then the subs are tending to be overexposed...blooming of bright stars, data and skyglow.
Thus irrespective of how long or short your subs are...you should be aiming for
this type of histogram (yep I know its about slides and scanner histograms but it's pretty much the same for astro pics). Of course trial and error and experience will give you an idea on how to achieve this.
Hope this adds some clarity.