hardie plank siding minimum length
Is it less than an inch long? I would keep the window trim and corners consistent throughout the home,although there can be exceptions, but I would strive to keep all details the same, and if it takes short pieces of siding to do so, so be it...

The siding you plan on using can be easy to break at the corners, let alone what a small piece will do. Using a small diameter masonry or glass bit, pilot the hole where the nail will go in. Hardie (r) siding is hung from nails anyway hidden by the next course of siding.