Canon or Nikon DSLRs?

500 ms.

That anyway depends on the type of format, on the existence of supports (e.g. a wall on which lean) and of properties desired in the photo: If you want a good microcontrast and resolution, you have to go even below that, otherwise you can dare a little more...

 

500 divided by focal length in millimeters.

For example, the Canon 5d mkIII resolves about 100 line pairs per mm at full contrast (0% to 100% luminance at adjacent pixels,) which gives an effective resolution from full black to full white of 15 arcseconds with a 50mm lens {[(lp/mm)/1000 ]*50}/206.265

The Earth rotates at 15.041 arcseconds per second, therefore an exposure of 10 seconds or less will give a clear picture.